When they try to hack into your Facebook Account
The IP address you see is the source IP address Facebook logged when someone logged in. If that’s a wireless (3G,LTE) connection, this IP will probably point to the ISP they were using. If they used their home broadband connection, chances are that you will be able to tell the city they are from. It is worth mentioning that their ISP would know exactly where this IP was located at that time (some are dynamic and constantly change)
That being said, there are a number of ways how to hide the IP effectively by using VPNs, proxies or just public internet spots.
But the police can trace IP addresses even when they are using a VPN!
Facebook does not provide any IP address, your IP address given by your ISP which can be Mobile ISP or Internet ISP. Yes, Police can track your accurate location with IP Address