To be honest, I've kind of disassociated myself with social media in general these days, the only one I use any more is LinkedIn and that is for professional reasons. I've got plenty of other projects to keep me busy :)

The only advice I would give is this: Facebook started in a densely connected community - students at single college - which allowed it to grow fast. So one possible strategy for a new network would be to find a similarly connected community and introduce it there.