What should I do when I see someone I recognize from Facebook, but have not actually met in person?

You could just say "Aren't you a friend of so and so," and introduce yourself. Just say that you recognized them from the friend's pictures. I don't think that is too weird. Could be a good way to meet a new friend and you can all hang out together then :)

Now if it's a friend of a friend's friend, then I'd say just pass by. That is pretty creepy.

I agree with Christine. If it's a friend of a friend, you could just smile and introduce yourself "hey aren't you friends with Bob?"

Between facebook and myspace, I think it's becoming common to run into people that you've already "met" online. We're all in the same boat. I don't think it would be weird.

Now if it was a friend of a friend of a friend, then I wouldn't say anything. You're too far removed.

Plus, if they're good friends with one of your good friends, then you must have something in common. It's always nice to make a new friend.

You might stop them and just say something like, I know this sounds crazy but you look so familiar to me. And, then ponder where you might have seen them and then suddenly realize where it was. I bet you strike up a conversation with the person and it could become really interesting!

Don't be shy! If you spot them, give them a glance and a sudden hello. And interrupt them and ask them if its really them; then introduce yourself. You won't believe how wonderful it feels to them that you recognize them on the street. You'll feel like a hollywood celeb, too.

if it were, I'd be glad if you said hello,

even it's a simple gesture and few words are exchange between two people that are strangers or acquaintances of friends the greeting in itself is thoughtful, u could always continue the conversation by saying hello again on line afterwords like "hey, remember me, we bump at so and so or met on such day" that would definetly brighten someone's day