My fc leader and I would scout starter cities for new players and help them out. When we found ones that we liked we would offer them an invite to the fc, if anything to at least make use of the buffs, but we would also tell them that they are free to leave if they decide we aren't for them and that we can still be friends after. It really helps when you try to be personal about recruiting and it really helps if they aren't burdened with the obligation of staying because they received help a few times. Once you start to get enough people they will start to bring friends and your fc will grow.