From the Model Mayhem FAQ:

How can I get my work removed from Model Mayhem?
If you are a copyright holder and would like your copyrighted work removed from Model Mayhem, you will need to file a DMCA with the Model Mayhem's legal department.

Once the legal team has reviewed and approved your DMCA request, it will be forwarded to the Model Mayhem team and we will work to remove the content.

Our DMCA processes are outlined here: