Your close depends on the situation, the environment. So how do you actually get their facebook?
It seems strange to me as the girl would have to tell you her full name, whereas if you ask for the email then it kinda seems less invasive.... or at least I thought.
Might give this a try, see what happens.

Yeah dude heard so much stuff about Facebook cold approaches, I would have thought the reply % was less than 1%.. unless you have a keen eye for sluts.