Best Social Network Sites and Best Methods

Are there any worthwhile social network sites other than Facebook, Myspace, and Twitter?

I assume there are probably already guides. What are the best ways to build up these accounts (of course you pretend to be a girl).

Links to guides?

technically, any place that allows you to post comments is considered a social network. With that said there is... (take out the * of course).
There are others, but these are BIG and missed sometimes especially ytube. It's considered authority.