There’s a couple sites that allow IP lookup, although this will usually just point you to their ISP (service provider). However, if you have documentation of the IP and the unauthorized access to your facebook, you can give this to their ISP through fraud / abuse departments and they will often shut off that person’s internet and / or pursue criminal charges on their own depending on the amount of evidence and severity (in this case not very severe). Worth a shot though, will get that person out of your account when their ISP calls them and mentions potential consequences.
If they won’t even look at your case, try calling your local PD and just saying you’re concerned someone is accessing your personal accounts and are unsure to what extent you may have been hacked. From there give them the documents and they’ll follow up with the ISP or point you to someone who will. It’s a valid concern. I’m also the vengeful type though, so I’m definitely the type to spend a few hours exacting justice.
Unless you are actually defrauded of something, I’m somewhat skeptical that the police are going to put this anywhere near the top of their priority list. Not that I have any other ideas, of course.