Dear Mr. nyan
I understand how you feel. They are using your art in a profit website. The man doing this is not a fan. The man doing that is a thieve trying to make money from other people's work.
I investigated a little bit about adult-empire. As it seems, it's not the domain's (adult-empire.com) fault per se, but t is the fault of a single user.
It is as following: you can create an account in Adult Empire, you upload the erotic art and you get some money. So there are many people there who post their own art (honest artists), but there are also a few thieves who take advantage of someone else's art (like the one who posted your art).
You can read this topic in a forum that clarifies it: http://gfy.com/showthread.php?t=1020223
The good news is, you can have your art removed from the website. You must follow this link: http://cs-ae.com/support/?group=users
There you chose "Submit a Ticket". Then, under Select Department, you chose "Abuse" and you click over "Next".
You'll be redirected to a new website. You complete the form with your request and you submit it.
That should be enough to have your content removed, I believe. I can't say for sure though.
If you can help me to keep browsing your works or if you have any other question you can write me at firstname.lastname@example.org
Thank you for your kind words