not sure if any are aware of this feature on the Facebook, but i had to share since most on here are creeps and this could help you out
in settings there is apparently a "find nearby friends" feature that allows you to do just that.
for example, you spot a lil shorty at starbucks, barnes and noble or walmart. doesn't have to be any of those places specifically. those are just examples
well if he or she has this feature enabled and you do too, they will pop up on people you may know.
happy stalking