If there is no parenting plan or court orders in place, then you cannot make the child come home if he is with his mother without going through the court system.  Your option, at this point, is to petition the courts for orders which grant you custody of your son and set out a parenting plan.  If the "run-a-way" tactic has worked once, your son is likely to try it again.  To prevent this type of gaming in the future, you really do need some formal orders in place.