Actually, I was looking to ask the same question. I know of about 20 or so, but looking to see if there is some master list somewhere with basic reviews etc. We are looking for lots of community interaction on our new sites.
http://en.wikipedia.org/wiki/List_of_social_networking_websites with the help of this link you can see list of social networking sites.
Just say the wiki list... Never knew there were so many of them... I can only imagine there are many more who haven't made it to that page...
How many there are isn't that important. However, knowing which ones your target audience uses is the big question. Sites such as Facebook, Twitter, Pinterest, Reddit, Flickr, StumbleUpon, etc. are the ones you should be focusing on. There may be thousands of social networking sites out there, but if they don't have any users, what's the point?
There are more than 200 well known social networking websites are there on the internet. Most popular social networking websites are facebook , twitter, badoo, google+ and more.
Cannot give an exact answer as there are thousands of them available and constantly adding more daily.
There are lot of social networks online. But just find and use only the social networks that you think it gives you the qualityof interaction and sharing thoughts with other people all over the world.