Agreed with above, I had that problem in 1.0 because nobody really talked to anyone. There isn't much you can do to keep them logging in. Again, while helping others, try and get to know them abit before jumping to add them to your ranks. People who aren't going to stick around make it painfully obvious.

Just keep at it and slowly you'll bolster your ranks with quality players who will stick around and help you maintain an active FC.