This is the most important thing to do whenever you find stolen work online.
Here's the DMCA notice page for AdSense websites, please everyone who finds their work stolen fill this in for the offending sites:
https://www.google.com/adsense/support/bin/answer.py?answer=146178

ETA: It is also expressly against Google's AdSense policy to have their ads on a site that violates copyrights, so it is a good idea to also send a "The site violates AdSense program policies in other ways." complaint through the report link so you can let them know that it is a Warez site existing solely to distribute other people's copyright material.