How do I find out who has blocked me on facebook?

That's one of the functions not provided but Facebook. You cannot be notified when someone unfriends or blocks you or see who did those things. Although blocking is confidential, which means that users are not notified when they are blocked and people cannot distinguish from their account between someone that blocked them and someone who abandoned Facebook, there's a way to know if you were blocked or not. If you can see that someone's profile is still visible from one of your friend's account or from outside Facebook, i.e., by people who are not Facebook users, you will be able to deduce that this person didn't delete his account, and that therefore you were blocked.

if you do a search for them and they dont show up, they blocked you. I dont think you can see a list of people that block you but that way works if you have a suspision dont bother making a CREEPER account, that is just scary. how many blocks could one possibly get? if they dont show up with a search they blocked you. people don't just Delete their facebooks. its not an instant process anyway it takes forever