How can you trace someone?

[Cherry]

I had a boy back in 2007 with my ex partner and my ex has disappeared off the face of this Earth, He hasn't paid me child maintenance since 2009 and even the CSA can't trace him. I would like to find where he is, not just for the money he owes me, but it is inevitable my son will start asking about his father, and if anything happens to him or I need to know any health questions etc. He has a Facebook profile, but there is no way he would add me or give me any information on his whereabouts, so I'm wondering how to do this covertly, and his profile is set to private. I also have reason to believe he is in Poland, as he was not only obsessed with the place, according to the CSA, they can't trace him via the Inland Revenue, and he wasn't the type not to work when I knew him, one of the many reasons we split being he was a workaholic. Any hints, tips or suggestions would be very welcome.