I have played FH with friends I already knew prior to FH even existing, but I've never, sadly, met anyone that I've become friends with purely through the game. I am part of a group / pack in FH as of yesterday but only starting to get people in there so maybe I'll get to make some new friends there :3
I have known people to have met in FH and have gotten into relationships of all sorts, romantic and friendship alike, though, and at the time (I was perhaps around 13-14 years old) I found it quite peculiar. I still do to an extent but not as much since it's no longer a new thing to meet people online, I suppose.