I didn't have that part, but was glad to see the elder in charge of it didn't ask for people to raise their hands. He just asked rethoriaclly ("How many of us have..."). While I see TheSheppard's point, I think is better to avoid things that may be construed as 'spying' (as this post shows it might be the case).
With some notable exceptions, I don't think elders are setting up anyone and trying to find out who has a FB account with that kind of questions. It's just an 'easy' way to introduce the subject.
I do know of elders setting up a 'fake' FB account just for spying on others. Sad life!