This is the problem for me right now. I don't have a plan for replacing the social contact of facebook (and facebook isn't giving me anywhere close to what I need). I'm also struggling with depression right now and pretty socially withdrawn. As soon as the current blues pass and I'm able to come up with a real life third place [1], I hope to start limiting how much time I spend there and eventually quit altogether.
[1] From the article - https://en.wikipedia.org/wiki/Third_place