The Internet has been pegged the Information Superhighway -- a place where one goes to find information on just about anything. But with the rapid proliferation of social networking sites, it has become the Conversation Superhighway -- a vast global dialogue between old acquaintances and new.

On social networking sites such as MySpace, the giant among them all, people can register their profile, keep in contact with other friends registered on the site and make new ones, look for long-lost acquaintances, build a fan base for a band or extend a network of business contacts.

In the four years since their launch, MySpace and Facebook, another wildly popular social networking site, have expanded rapidly, becoming the busiest hubs on the Web and changing the way we connect with others while re-defining the concept of community. Traffic on these two sites soared last year, with the number of unique visitors jumping 270 percent (from 14 million to 52.2 million) at Facebook and 72 percent (from 66.4 million to more than 114 million) at MySpace between June 2006 and June 2007, according to a comScore Inc. survey of popular sites.

Who are all these people and what are they doing? According to a study commissioned by MySpace that surveyed 1,000 people ages 18 to 24, there are six personality types who regularly use social networking sites:

• "Netrepreneurs" use the sites to take advantage of their money-making potential.

• "Connectors" like to share information and links with others.

• "Transumers" join to find others who share their interests and hobbies.

• "Collaborators" create and promote events.

• "Scene breakers" are looking for new scenes and places to be.

• The last, and most common, are the "essentialists," who use these sites to stay connected to their friends and families.

Social networking isn't just a U.S. phenomenon. It's everywhere, with different sites serving as the major players in different geographic areas. MySpace and Facebook dominate the United States, while Bebo is popular in Europe, Friendster in Asia-Pacific and Orkut in Latin America, according to comScore's World Metrix measurements.

MySpace launched officially in January of 2004 and had 5 million members before the end of the year. In 2005, Rupert Murdoch's News Corp. bought the site, which is now part of Fox Interactive Media and now gets more traffic than any other site in the country: 25 percent of all Americans are now on MySpace, according to company figures.

In addition to its social-networking features, the site has grown and evolved into a one-stop source for music, movies, blogs and groups devoted to specific hobbies and interests.

As it has grown, so has its ambitions. MySpace launched a voter registration campaign in 2006, an original Web series ("Roommates"), the "Transmissions" music series, the MySpace/MTV Presidential Dialogue and, last year, the Impact presidential poll, which is designed to reveal political views of younger Americans.

Whether it's deciding what to do on the weekend or promoting new music, "MySpace makes what [users] do in the offline world a) more efficient or b) more interesting," MySpace co-founder Chris DeWolfe told Forbes.com when he was asked in an interview how the site was able to lure millions with the usual marketing or advertising. "If you have 10 friends, and nine are on MySpace and you're not, you feel pretty left out. People end up joining sooner rather than later."

Facebook originally launched as an online resource for Harvard students, when it was founded by Mark Zuckerberg, Dustin Moskovitz and Chris Hughes from their Harvard dorm room in 2004. A month later, it expanded to Yale, Stanford and Columbia, and then extended to all college campuses, Last year, it opened membership to anyone and now has more than 60 million active users.

Facebook is described as a "social utility," as opposed to social network, because it's designed to be an efficient way for people -- largely members of the student and professional communities -- to communicate.

While Facebook and MySpace get most of the attention, there are many other large and small social networking sites. Some are general social sites such as MySpace, while others are focused on specific topics such as gaming, genealogy, music, books, sports or professions.

Friendster, for example, has more than 54 million members, mostly young adults in their 20s and 30s. Many are singles looking for dates, relationships or friends.

Community Connect Inc. is a social networking company that has launched five specialized sites aimed at specific ethnic groups: BlackPlanet.com (African-Americans), MiGente.com (Latino), AsianAve.com (Asian), GLEE.com (gay and lesbian) and Faithbase.com (Christian). The company was founded in 1996, and its first site, Asian Avenue, was launched the following year. The five sites have a combined membership of more than 20 million, with Black Planet by 2005 becoming the largest African-American social networking site.

Community Connect "was founded around the premise that there's an opportunity to engage people in an online model of community facilitated by technology," says Kay Madati, the company's vice president of marketing and communications. "We built our platform around the idea that niche audiences on the Web can coalesce and engage around the issues of culture."

Bebo is a popular United Kingdom networking site, with an emphasis on entertainment and on providing a safe online experience for younger users.

That's a problem that MySpace addressed just this week, adding security measures in 45 states, including Pennsylvania, aimed at blocking sexual predators.

Among special-interest groups served by social sites, readers can find the equivalent of an online book discussion group, with which they can share book recommendations and join discussion groups. On Library Thing, for example, members catalog their book collections online and meet others with similar literary tastes.

Online social networking has become a phenomenon that goes far beyond meeting others.

Now that many of these sites count their active members in the millions, they've become a force in media, entertainment, advertising and marketing as a way to reach large audiences, especially the elusive younger demographic: Advertisers looking for the 18- to 30-year-old crowd are turning to social networks.

Musicians and entertainers have found sites such as MySpace to be an effective way to build an audience: Lily Allen, Sean Kingston, Arctic Monkeys, Colby Caillat and Dane Cook are among artists and performers who have used MySpace as a career launching pad.

As an advertising vehicle, social networking sites are still in their infancy but have huge potential, Community Connect's Madati says. Instead of pushing a message through traditional mass media, "Advertisers will have to learn how to interact with this new generation."

Social network members are a receptive audience. Instead of putting out a message and hoping it will be heard, advertisers can now be "invited" to share their messages with a receptive audience. But, he adds, it doesn't spell the death of the 30-second TV spot, which is still the most effective way to reach a mass audience.

Madati says it's impossible to predict where this is all going -- whether a site such as MySpace will just keep getting bigger and bigger, or whether something else will come along to take its place.

"What I do know is that technology-integrated communication will continue to be a part of our lives. Its core essence being the idea of connecting people won't go away and will continue to proliferate.

"I think this is the most interesting change in how consumers and brands interact with teach other, and how technology is changing that. Consumers are really in the center. They've changed the game."