1st. Girls that reply with short, closed ended sentences - BAIL.

2nd. Get them to add YOU on facebook. e.g '...let's take this over to fb, much easier. put ********@hotmail.com into fb search. maybe catch up on there x'
Getting them to search using your email registered to your fb account eliminates the excuse of not being able to find you because there are so many 'Joe Bloggs'.
If they are interested in you any more than replying to your pof msgs just for the sake of it, they will add you. Otherwise, be grateful you saved yourself a shit load of time that i'd bet 50 to 1 would have been wasted getting nowhere.