There's a social network for every interest (this list gives you an idea). Below are some of the most popular.
What is social networking?
Social networking is a broad term used to describe user interaction and community building that takes place online. Examples of social networking sites include Facebook, LinkedIn, and MySpace.
Why network online?
Connecting with friends, family, and colleagues online is a great way to keep up with the latest news and trends. You can share information like links, photos, and video with one or more people, all from one place.
What about privacy?
While social networks make it easy to share information quickly, they also have increasingly provided ways to share selectively and carefully. But it's easy for your information to get away from you. Keep in mind that once you're information is "out there" it can be difficult, or even impossible, to get it back.