For example, synnabar's original.
IMVU is a "Second Life"-ish chat program. You can make and sell virtual items and get credits to buy other virtual items but I'm not sure if they can aslo cash out credits into real money so the thief may or nay not be making money off this. Either way they shouldn't be taking other people's work and the original artists should be notified.
I already contacted Synnabar myself, but if others recognize stole artwork I encourage you to send a note to the artwork's original owners. Thanks :)