I am going through this right now, my ex gf has moved 4 times in the last year and a half and each time i had to search to find out where she is. I now have obtained custody ( i got her on 4 random drug screenings and i am on my way to my pretrial today at 1pm) but untill i could get custody she sat in front of the judge and said i threatened to kill her boyfriend, and i showed up drunk and caused a ruckus"". Niether of which is a reality, they made me meet her down the street at a sheetz to do the custody switch. Good luck on that. But all i can say is a little legwork, goto the Post office and chane your childs address and foreward it to your house and send him some mail. then you will get the address because all they will do is slap a sticker on it for a couple of weeks while thye forward it. its a dirty trick but it works. Or sometimes if you are charming enough you can get the forwarding address from the post office.