Phpbb IP capture question

I'm looking for a website or something fairly simple (I'm not too savvy) that i can PM a user of a forum and when they click the link i can retrieve their IP. ie ----> Create an account with a website for this sole purpose, get a link of some sort from there, PM someone on a forum i am a member of, when they click on the link, i can go back to my account on this website and retrieve their IP.

Reason: Some jerk is harrassing me on a forum, i'm pretty positive it's a normal user, if i can get their IP, i can look up where from, and avoid this person. Any help would be great, thanks! :)