One of the least advertised Android functions is locking remotely the phone with the capability of providing a way to call you back as soon as someone finds it.
In 4.4.x versions it is already built in. For previous firmwares it is available for free HERE.
The device manager has 3 main functions and its URL is https://www.google.com/android/devicemanager
Ring: This is in case the phone is in manner mode and you are sure it is close to you. It will just simply make it ring.
Lock: It will let you set a new password, provide a message for the person who finds it and a phone number so that once it has been found someone can call to that number.
Erase: Wipes all data (contacts, media content, etc). It will reset the phone and once performed, device manager won’t work until the phone is synced with your Google account again.