How can I find the new phone number of someone that has changed it?

My ex left me with an unfinished lease and no rent money. He took my truck and changed his phone number so I can't find him. Is there any way to figure out his new number? He has Sprint but the plan is in a family member's name and I can't get through to them. Please help!How can I find the new phone number of someone that has changed it?
UNDER NEW STALKING LAWS





NOPE U AINT GETTING JACK SHlT !How can I find the new phone number of someone that has changed it?
Call 411 and more.
by using telephone directory



by the means of news paper



if you know any of his friends or relatives



his address, if you know or place he usually visits



email him in case u know his id