ADORA MORA, Student: "Hi. I know you're probably wondering who this may be."
JUDY WOODRUFF, NewsHour Special Correspondent: Eighteen-year-old Adora Mora is reading a message she received on her favorite Web site for socializing.
ADORA MORA: "I know your sister Ebella (ph). When I searched her last name on Facebook, I also came across your page."
JUDY WOODRUFF: For millions of young people like Adora, responding to messages like this one has become an easy way to make and sustain friendships. Before arriving at Harvard University to begin her freshman year, Adora has already connected online with a number of new "friends."
So how many in the freshman class at Harvard do you already know?
ADORA MORA: Probably around 50. How many do I talk to on a regular basis? Maybe around like 10, you know?
JUDY WOODRUFF: Really? Already?
ADORA MORA: Yes. Yes. I got kind of addicted to it last month. I would do it everyday.
JUDY WOODRUFF: These Internet social clubs, known as social networking sites, allow users to join for free, create personal profile pages, add photos, music, blogs, and messaging, and, with no geographic boundaries, build their own network of "friends," people they already know or may never meet, who willingly share their lives on the Internet.
Kevin Maney covers technology for USA Today.
KEVIN MANEY, USA Today: If you can imagine having a club, a social club, where everybody walked around with a big sandwich board on the front of them saying everything about themselves, if you take that concept and take it to the Internet, something that's happening electronically across the world, not just in one little building, that's kind of what social networking does right now on the Internet.
JUDY WOODRUFF: Whether at school or at work, young adults, like Alesha Hardin, access their online social networks throughout the day.
ALESHA HARDIN, Young Adult: If I'm going to sit here for a full day, if I'm on the phone, I'm checking it. So I can check it up to five or six times a day when I'm working because, you know, as you can see, I have to multitask when I'm doing something.
JUDY WOODRUFF: With more than 200 competing sites, social networking is more than just chatter. It's become big business.
So would you call yourself a computer geek when you were growing up?
MARK ZUCKERBERG, CEO, Facebook: Oh, absolutely.
JUDY WOODRUFF: Two and a half years ago, Harvard sophomore Mark Zuckerberg and his two roommates came up with the idea for Facebook, a Web site where students share photographs, messages and information about themselves with those in other Harvard dorms. It proved so popular that, within a few days, over a thousand students were accessing the site.
By the end of 2004, Facebook expanded to almost 300 schools, with access granted only to those with a valid college e-mail address. Students in one school could now befriend students at another, expanding their personal network of friends. And with privacy controls, they had the option of limiting access to their personal information.
Today, more than 2,000 colleges and 22,000 high schools are on board. And this past summer, Facebook expanded yet again, allowing 15,000 corporations, nonprofit groups, and members of the military to set up their own networks.
MARK ZUCKERBERG: Up here is everything except product development and engineering.
JUDY WOODRUFF: Mark Zuckerberg dropped out of college, and today the 22-year-old executive in flip-flops and a t-shirt heads a multimillion-dollar company, with a staff of around 150 people, most close to his own age, and a business that has grown to more than nine million members.
MARK ZUCKERBERG: I'm really young, so I have to be thinking about the long term, you know, and how the stuff is going to play out. And I think that the way you achieve the best long-term value is by building real value in the world.
You know, so we focused a lot on our product. And what do the people who use the service get out of it? Are we actually helping them achieve their goal of understanding the world? And if we can do that, then I don't think we're going to have a hard time making a lot of money.
JUDY WOODRUFF: Facebook recently announced that it would no longer limit membership, making its social networks available to anyone on the Internet, and matching the open door policy of networking giant MySpace.
With over 100 million user profiles and over 80 percent of the social networking market, MySpace is now the most visited Web site in the country, ahead of Google, auction powerhouse eBay, and longtime industry leader Yahoo.
And online advertisers have taken notice, spending about $280 million this year on MySpace, Facebook, and their networking competitors, in an attempt to reach the lucrative youth market. It's a figure that some experts predict could balloon to nearly $1.9 billion by 2010.
JANE BUCKINGHAM, President, The Intelligence Group: How many friends or contacts do you have on MySpace?
SOCIAL NETWORKING USER: I probably only have, like, 200, maybe, not too many.
JANE BUCKINGHAM: So 200, but that's not too many?
SOCIAL NETWORKING USER: Well, probably only like 100, maybe, are, like, really good friends, though. So, like, a lot of them are kind of like people you know, not like you talk to them all the time.
JUDY WOODRUFF: Focus groups, like this one, help marketing consultants like Jane Buckingham develop strategies for advertisers interested in the youth market.
JANE BUCKINGHAM: There are their close friends, and then there are the 2,000 people who they talk to on MySpace. There's that feeling of, even if I'm not super-popular in my highs school, I have, you know, 1,000 people who want to talk to me, so I can't be that bad.
SOCIAL NETWORKING USER: You can kind of judge people based on how many friends they have. You know, it sounds kind of mean. But, like, people who have 1,000, you're like, "Ew, they're weird." People who have, like, 300, you're like, "Oh, OK."
RADIO ANNOUNCER: If you think "MASH" is or ever was funny, I swear to God, you are way too old to be listening to this show. "Gen-Y U." on 103.7, Free FM.
RADIO HOST: All right, San Diego, what's happening? This is "Gen-Y U" radio.
JUDY WOODRUFF: On their popular "Gen-Y" radio program in California, Brent Williams, John Fiske, and Kris White debate issues of interest to their generation. Today's topic is MySpace.
Why do you hate MySpace?
RADIO HOST: I think it's just a shrine for yourself where you can go online and go, "This is what I did this weekend. Here are pictures of me." Everyone come to my page and look at me...
RADIO HOST: A tribute to yourself.
RADIO HOST: ... as a tribute. Yes, that's just stupid.
And then people make the argument of, "Oh, I get to keep in contact with people that I lost contact with." Generally when you lose contact with someone, there's a reason for that. And if you want to gain contact, then -- like, we were saying, don't just e-mail, "Oh, you got an invite from this person to be your friend."
RADIO HOST: But it depends on the person.
RADIO HOST: How about pick up a phone, and call them, and say, "Hey, I haven't talked to you for a while, and I care to get in contact with you"?
RADIO HOST: But it depends on the person. Some people's MySpace page is a tribute to themselves...
SARAH MCGARITY, Young Adult: I don't have a MySpace page. I think that's a little too open, because it's for everyone.
So what classes are you going to take this quarter?
JUDY WOODRUFF: For some young people, like Sarah McGarity and Jesse Jones, the issue isn't about self-promotion or friendship. It's about safety.
JESSE JONES, Young Adult: At first, it was just a friendly way to, you know, say hi to friends that maybe you haven't seen, meet new people. Now it's turned into this terrible, you know, thing that, you know, predators are looking for young women, and women, you know, may not, you know, know better and that -- you know, things happen.
JUDY WOODRUFF: A recent survey by the Polly Klaas Foundation found one out of four teens say they have talked online about sex with someone they never met in person, while nearly 20 percent reported knowing a friend who has been harassed or asked about sex online by a stranger.
ALESHA HARDIN: I get MySpaced all the time. Like, "Oh, baby, you look so hot." And like, oh, you can really tell that from, you know, a little five-inch picture.
JUDY WOODRUFF: In the wake of a number of reported incidents, including alleged sexual assaults, and mounting concern over open access to personal information, MySpace has added privacy options and beefed up its security. And many young people have started to censor what they post.
ALESHA HARDIN: People of my generation don't realize that your employers are searching for you on MySpace to see what kind of lifestyle you lead before they hire you. You really have to watch your back.
DOAN TRANG PHAN, Social Networker: Well, that's why I have my profile on private, because I have a professional job. And the last thing I need is for my employer to be able to pull up and see a picture of me going out partying or something like that, because it's not a professional image.
JUDY WOODRUFF: Despite these concerns, online networking continues to gain traction among young people and capture the attention of big business. Last year, Rupert Murdoch added MySpace to his News Corporation empire, paying a reported $580 million for the leading Web site and its parent company.
For its part, Facebook's open-door policy may make it more attractive to potential suitors, the subject of takeover rumors for months. The Wall Street Journal now reports that Facebook and Yahoo are discussing a possible sale for close to $1 billion.