I have to say that a facebook close can be just as rewarding as a number close. My friend has close many girls from a FB close. Or you could follow this method that I have used and turned a FB close to a true number close:

Me: So whats the best way me and you can stay in touch?
HB: Ummm do you have facebook?
Me: Yeah, hang on let me enter it into my phone or I wont remember. So whats your second name (assuming all uve got is a first name).
HB: Ok its (enter name here)
Me: Sorry I didn't get that.. (music too loud, strange name spelling etc)
HB: (........)
Me: Ya know what, just tap ure number into ma phone, would be much simpler and i can get ure fb off you later (defused)
HB: Ok!

This has worked for me a few times now, but feel free to change bit to suite.

atb

Adz