this is exactly the reason why Facebook allows people to file complaints when their identities are being used fraudulently, that is pretty much only thing you can do because facebook will never reveal user's IP to other users because it is a matter of privacy unless you have filed official reports for the proper authorities such as NBI Cyber Crimes Division, but since it's just a fake account I seriously doubt the NBI will do anything, so your best option is actually just to file a complaint with Facebook