If your phone was stolen and the thief turned it off; or did it a factory reset, it may be impossible to recover your phone through the previous methods already discussed. Your best shot at finding your lost phone is through its IMEI (International Mobile Equipment Identity) number and you may need the help of your network operator and the law enforcement agencies to get this done.
You can also track your IMEI number through a database of lost and stolen phone. Computer village launched a unified database for this a few months ago. You can find your IMEI number on your phone pack, behind its battery or simply dial *#06#.