You laugh and joke, but if you don't find a way to move users from social networks to forums (and by paying a little, it's the solution that everyone likes) it's practically impossible to open a new forum.
I have over 100,000 users in my Facebook groups (and pages) and a site that gets over 250,000 views a month on the topic you want to forum for.
No one will marry from facebook especially if the forum has no posts and registered users.