I think the key is to start building relationships. Get yourself "out there" and maybe do a favor or two for people. Get to know people, socialize (at least virtually).
Go the extra step. I doubt there is much worse for a potential JV partner to just get blank "JV" requests in their inbox when they don't know you. Until I started getting them (JV requests from people I don't know) I didn't realise how annoying it could be.
So take the time to get to know people here, it's a great place for JV's.