By Douglas MacMillan

A dozen social networks, each with a different society in mind

Facebook's rise from exclusive online hub for Ivy Leaguers to global digital directory has inspired a countertrend: niche social sites. Name an affinity, hobby, occupation or demographic and there's likely to be a dedicated social network for it. Puppy lover? There's Dogster. Game-happy teenager? Try myYearbook.

Most interest-specific sites are small, but they add up to a sizable portion of the social Web. In July, at least 280 million people logged on to social sites other than Facebook and Twitter, according to audience tracker ComScore Inc.

In this Bloomberg Businessweek slide show, take a peek inside a dozen social sites that target certain types of online networkers.