Help please

I'm putting this in a wrong category but I just need answers so I left my phone on a desk then when I returned back to the desk my phone was gone . I asked people around me they said they didn't see my phone. The person who took my phone turned it off which is how I know it is stolen. I pressed find my phone but it can't track unless the phone is on. I reported to deans of my school but all they did was make me file an report .. btw if it's helps I have T-Mobile and had the phone for a couple months now.