If nothing else, and it is not the admins of said community using your map, you could send a message to the community's admins informing them of the plagiarism and hope they do something about it. Although it was not a map, I had someone use some of my art as their own with no attrib. When I messaged the admins, they pulled the art down and blackballed the individual. In another case, I was attributed with the original work although they changed it to fit in their usage. I am always fairly with others using my stuff as long as attribution is made.

And as Ascension said, it is difficult at best to constantly search the web for any use of your stuff. Back in 94 to 98 when the WWW was still fairly small, it was easier. Now, it is damn near impossible. The only solution I see is to place a watermark where it is very difficult to remove. I for one will always ask to use something before I actually use it. Or, in the least, I will attrib the work with a link to the artist's gallery.

rmfr