That is an absolutely horrendous situation to be in. While I can see how it can be a compliment someone copying what you've created, I've never quite thought how it can backfire THIS way (search engine rankings)...
Believe it or not, publicity is a strong tool to fight against theft. Over the many years I have seen a lot of cases in which hosts would publicly expose such artwork/content thieves. It would eventually catch their attention and they would immediately take down the stolen content, or better yet - the whole site.
If you aren't comfortable exposing them on forums, you can contact me in private and I will happily help you by sending them a message about it personally. As a media outlet, that kind of message carries more weight.