if they are using a vpn or proxy there is a good change the ip is listed online.
even with an ip, if you trace it, traceroute it or whatever, your not going to get too much info on someone with it, unless you have some skills and presumably they are using a static ip.
perhaps logs of the ISP of who ever had that IP on the time whatever incident happened to you would be the best way to get info, but good luck with that.