Is it possible to wipe out the memory of a missing ipod?

I was at a quince and my little sister lost my ipod. So far my facebook has been hacked and whoever has it has been messaging ppl creepy stuff. I heard about MobileMe and tracking it down but i never got a chance to download it on my ipod ): is there any other way i can find it or clear the memory?? go to apple store? call cops?? idk