also of course i would only ask a girl out if she was single!
Most Helpful Girl
hmm if you know the girl personally and you start chatting and she is also actively involved (by asking you questions back or something) not just giving one word answers you can definitely ask her out
but adding a random girl with a pretty pic and start chatting is a bit creepy and comes of as desperate in my opinion (a few guys did that and i was always like wtf?)
Most Helpful Guy
Sure, you can, but Facebook is more connection between mutual friends.
Meaning, the more friends you have, the better chance of you hooking up due to its mutual friend's search engine.
If you're not a very popular guy, You're better luck developing better social skills and lady skills because I'm an asshole for assuming, since you rather online date, you don't have much of those said skills.
Good Luck man ! ;P