The way it is supposed to be done is with a DMCA complaint, and I don't think you can do that unless you own the IP in question. Or are you saying that they are ignoring DMCA complaints? That is a much more serious accusation.
Android Market has a 'flag' button that lets you specify, eg, that 'Wolverine' isn't anything to do with Marvel but uses Marvel characters and artwork. They ignore this and similar copyright infringement flags.
You have to own the content to file a DMCA complaint.
