How to setup a meet/date with some one you dont know very well via Facebook

Long story short I met this girl through a guy at work, its his family friend..

This was a while ago, and she had a bf then, but is since single..
So I've been flirting with her a fair bit in the past few days on her wall.
And it has been going quite well...

I've only met her once, and I'm pretty keen to meet up with her again, but we dont have any mutual friends besides the guy I met her through..

How should I go about setting up a date or just a casual meet up?