What to do to find my stolen IPhone 4s?

Today I found out my IPhone has been stolen. I put in the top shelf of my locker before I (locked it) went to class and when I returned, it was gone. I thought maybe I put in my bag so I dumped out my bag. Nope. My friend Maria and I searched almost all our classes but there was no luck. We called it. Nothing. My parents are furious at me but how is it my fault somebody stole it? They kept making the excuse for me to put find my friends on the phone (so they could follow me) in case of it getting stolen and they lost it when they hear it was gone.
So I'm not really sure what to do at this point. Is there anything? My dad canceled it I'm pretty sure (I don't know though because he won't look at me) but what else could I do!
Everyone is telling me this girl Beverly who isn't exactly trust worthy has it. They said she was acting weird and didn't show up to volley ball and it makes sense in a way because she does know my combination lock somehow. Just please, give me a suggestion or something. I'm desperate here.

Tell your parents to drive you to the local police department. There, they will walk you through to file a report and they will contact the school. After it is reviewed, they will recover tapes from the school cameras and they will be able to find out who stole it.

Go to icloud.com and sign in to your account. Then click on Find My iPhone and it should try to locate your phone and give a location on a map.

Well other than asking this girl about it, and or dumb luck, there's nothing you could do at this point. The app you should have installed was Find My iPhone. Think the name states what it does.