How to use the find my iPhone app?

Phone lost or stolen trying to locate

Sign into your iCloud account on your computer and click on Find My iPhone. If you have another Apple device that uses the same iCloud account, you can sign into Find My iPhone (or other device) on that device and find the other.

Did you have iOS 7 on it? If so then the thief can't wipe it or turn off find my iphone without your Apple password.