i got my nike backpack stolen what should i do?

[Zach]

my small nike backpack got stolen from me and the kid i know that stole it has it at school. i have not told him anything about it but i know that it is mine because he turned in my stuff that was in the bag. he colored it blue (the nike symbol) and i just dont know what to say to get it back. i know i can steal it back from him but i dont want the school getting involved and end up me being the thief