Tell your teachers and the principal, there are cameras everywhere in the school, make sure they check the cameras everywhere on the day you lost it. The cameras will catch the stealers and you can file charges on the thieves. Shit happens, take charge of your life son!
Honestly it’s probably been stolen. You can look around for it very place you can think of and them some but you most likely won’t get it back. That’s why I don’t bring it to school at all. It’s never been to school with me nor will it ever go with me.
Face it. Kids these days are greedy. If they see an Ipod chances are that they are gonna keep it for themselves. But It wouldn't hurt to look in lost and found or look in every place you were at. Good Luck ^_^