I lost my iphone, what can I do?

I left my iphone in the bathroom at school and someone took the phone after they found out. At first when I called the phone, it was ringing. After 5 times of calling, the girl who has the phone turned off the phone and it went straight to voice mail. I called again tonight and she turned it back on but then off cause I kept calling her. My iphone has a pass code so she can't go through it unless she restores my iphone. I don't have the find my iphone app either. D: What can I do?

Try buying a new one.

Go to iCloud.com and sign in and use find my iPhone! And you can add a password to it, locate it, and even wipe all the data off of it! Goodluck!

Go to a apple store they can track it if your location services are on an you can go from there

You should report it to your school security office. Call your phone company and tell them you lost your phone. If you have a SIM in your phone, you can also lock your phone. Your phone will require the SIM PIN code regularly to prevent fraudulent use. The SIM will block any service if the PIN is wrongly entered three times. Notify your service provider and give them both your mobile phone number and IMEI number. You can also prevent the thief from using your stolen phone with his own SIM. To do this though you need to know your phone's unique identification number, called the IMEI (International Mobile Equipment Identity). If you can also give this number to your phone company, they can block the handset from being used with a different SIM. In many cases, you can obtain your handset's IMEI by entering *#06# on your handset, but your phone may be different. Check with your manufacturer or user's manual. Note the IMEI and keep it in a safe place.
By the way, it may be useful to install some anti-theft or monitoring app on your phone. It may help us get our lost phone back in such cases.
http://ikeymonitor.com/