^^^^Yeah, what he said. It's certainly possible, but not on your own. You can't get a facebook user's ip address without:
A) The help of Facebook
B) A court order for them to give it out which requires a very good reason.
Even then, they wouldn't be giving the IP to YOU, they would be giving it to law enforcement if it rose to that level. If it's a simple case of abuse, they'll just warn the user or whack the account.
No web site is going to give out IP addresses of users to other users so they can start some kind of electronic retribution.