Content is King when it comes to SEO, you have to write keyword specific copy, of course on sites like social apps what pushes you to the top is mostly back-links and lots of them.
To get more users to register I suggest you create a Tour section where users can actually
see what you are offering before signing up.
Think about design as well, to be honest it looks like it was made 10 years ago, if a site looks iffy people aren't going to trust it and won't join no matter what you're offering.
Edit:
Had a quick browse up and signed up a account, you don't get any kind of confirmation when you send the form it just refreshes the home page?
Again back to the design, it needs
a lot of work. It's inconsistent and disjointed to say the least, the images all look like they are from word art or done in paint, the fonts are awful and the layout is all over the place.
Also why do you need a forum on a social site? If you are going to implement one though think about having your users automatically register for the forum with their site details. People are lazy and won't want to register twice, once for the main site and a second time for forum.
If you want people to join you're going to have to use word of mouth maybe at your school/college because you won't be getting many sign ups from Google.
This post has been edited by 4colourprogress: 03 February 2012 - 09:05 AM