Playing devil's advocate here ...
If it has no niche, then WHY would someone join your social network, over say Facebook? Does it have super unique features that you can't possibly find anywhere else? Are there people talking on it right now? What reason would someone like me have for signing up to an empty site about randomness where there's no one else to talk to? When I can instead spend my time interacting on a social network with millions of users who are going to read what I have to say and respond to me right away for instant gratification?
In short ...
Step one: Give people a reason why yours is better. There has to be SOMETHING different that can't be found anywhere else. DaniWeb, for example, is unique in that we encompass everything IT under one roof, and we group content together (news, discussions, tutorials, etc) within a single timeline.
Step two: Give people a reason to stay. DaniWeb gained popularity because myself and my friends constantly posted on the site day and night for a very long time. Slowly, other people chimed in, because they saw that there were people to talk to. And anytime anyone new joined, we all instantly started talking to them, giving them the instant gratification they wanted, even if we weren't big. Fake it till u make it -- We gave people the communication and answers they wanted just as detailed and just as fast as if we were a huge community. Slowly, we became one.
