The Famous Harness The Web

By Douglas MacMillan

Forget soft drinks and sneakers. These days, celebrities prefer to plug their profiles on social networks.

Oprah Winfrey fans swarmed Twitter in the days after she posted her first "tweet" on the microblogging site. Hundreds of thousands of hip-hop fans are taking to Ning, where rapper 50 Cent started his own social network.

But the benefits go both ways. Many of these sites have recognized the boost these stars give their sites, and several go out of their way to keep the celebs happy and coming back.

In this BusinessWeek slide show, we'll meet seven big stars who have become the celebrity "face" of different social media sites—and find out how the entrepreneurs behind the sites are benefiting as well.