How can Android Device Manager (ADM) help to locate Android phone if Google account's password has been changed?
Did you activate ADM with device administrators in the phone? If you do so, you could lock your device and no need to change the password.
But if someone is using your phone, they can reset your mobile with recovery mode. If they do so, you can't locate your mobile.
I think you should inform the police and they will looking for your mobile with the IMEI number of your mobile.