Its always written on the pack of the movile phone or trycontacting d store u bought it from most stores write down tg number foe ref purpose Mobile phones sends d imei no with d gsm no when making call so u can get from Ur service provider
There are third party apps u can install on the lost phone through Google play since its android its always coneccted to s gmail acct uses with it after installing d apps u just have to go to their website and track