Japanese language question. . .?

Question:

I was wondering how you'd say (for example), "Are you on Facebook?"
The "facebook" part of it isn't important, the point is, how do you ask if someone
belongs to any site where you have your own profile, etc. Do you use suru or yaru or something else?

Answer:

I'd say "tsukau (to use)", i.e. "Facebook tsukatteru?" (informal) or "Facebook wo tsukatte imasuka?" (formal).