Really, the only thing that can be done is to gather up evidence (forum posts and whatnot) that the sprites belong to other people, and then report the offending pictures to the dA staff. I'm not sure if that's been done yet, though (but with how many people that know about it now, I sorta doubt that it hasn't), and, just as a caution, I would advise people not to flame that person, or they'll possibly get into trouble as well.
They took one of my sprites, too - the one I made for Hawk0083 (and that he colored). Couldn't they have taken one of my better ones, for goodness' sake? :P