The only way is to put inside a GPS tracker, independent from the phone. Somewhere inside, on Internet is a service manual which can show you how to open your phone.
Write down your IMEI. It's the only way to find out a phone using only 2g. And have to be done by the police.
This can't help you if they turn off the phone and later they break the IMEI and clone/create fake one. (I'm not sure how it's working).
Samsung find my mobile is also a solution, but you must have 3g data nonstop on, and your phone on of course.
Sent from my GT-N7100 using xda app-developers app