Something that tends to work for me as an opener if I met a girl and got her name, but didn't # close is this. I send them a friend request and enclose this message in the request

"Hey this is "X" I met you at "Y" and looked you up on FB b/c I figured "what self-respecting girl between the ages of 18 and 35 doesn't have a facebook?"

They almost always accept the request and message me back. The last girl said

"Hey I am glad you looked me up, and you are totally right about the FB thing. Every girl has FB unless they ahve something to hide."

So now I am going to keep working it and get her number and set up a hang out.