@silverwizard if you can host a file on a site where you can look at the access logs and then post a link to that file, you might be able to bait them into downloading the file which could give you their IP address in the access logs. A whois search for the IP address.could get you their ISP and geolocation information on the IP could get you the general area.
That's a lot of "ifs" and "coulds", though.