what do you mean ?In the case of a referral only site, you are going to be relying heavly on your current members to send out invites. Also, making your forum to were people can apply for access is the best way. Then later they can be given the golden ticket. Just hope the content is worth staying.
I've once tried to invite FB people from a FB group I managed. It was mostly unsuccessful. What worked so far better for me is, if someone posted useful content on FB, invite them to post it also in your forums.
And, I would not recommend to invite people from groups that do not belong to you.
Just think of it this way: Would you like it, if others are trying to get your members to join a group with same/similar topic?
I might give a try , thanksIn a way it's the same, yes. However there are some fine differences. People that post useful content on FB might also be happy to post it elsewhere.
Inviting people that just comment on FB, might be less likely to join (more passive users). And there is a small difference in asking directly to join and asking to post. If you ask people to join, then they might feel that you ask them to be an active member. If you ask them to post something interesting they have posted already elesewhere, they seem to be mostly okay with that. Although they might not become regular members...Just give it a try and see what works best in your case.