If you came to know your mobile is missing, do not get tensed; there are good amount of chance that your cell might be near you. first you need to do is usually search near by, if you find your mobile thats great if not really, not to take tension and sit quitely and believe when have you made any call last and search at that position.
Track mobile phone through IMEI
IMEI is 17 digit number which is assigned to a mobile by its manufacturer which you can use for monitoring mobile phone
Samsung has this facility i think where they can help you locate your mobile device