i have experienced this situation .I lost my mobile when i was going to market i immediately reported to the network people and blocked the sim later on i got my duplicate sim.
immediatly i will call to that my mobile. If the person who got my mobile is good and honest one , he will surely pick my cal or else he will swtch off. If my mobile is switch off then i will make it block the sim. but there is some way to get our mobile number through pin number