NO!? Who in the right mind thinks that everyone should do something, because if it was my bike, I would want everyone to beat up the dude stealing it? What? Who thinks like that. Yes if my bike was stolen, sucks for me, but how is it anyone else's problem. I wouldn't expect anyone other than my immediate family or friends to do something if they knew/saw something happen. Why stick your nose in someone else's business, when it doesn't effect you at all?
What you need to do is take a step back and assess the situation. Yes it could be someone you know, but it also could be someone who you don't even know. Does this bike getting stolen effect your life at all? Chances are, even if it is by some chance, a friends bike. It' doesn't effect you at all. Yeah later on if you found out it was a friends bike or a neighbors, would they have done anything to stop it if they saw the same thing happen to your bike. Most likely no. Maybe call the cops, but that doesn't get anywhere, because its a fucking bike. Someone stole my cell phone I'd like to make a report! LOL. *Cop* ok we'll get right on it!