Smartphone Questions? Ask A Smartphone Technician for Answers
Well stopping the service to the phone is going to prevent it from being found.
The usual way to find it is by going to https://www.icloud.com/#find and as long as the phone has service and you had enabled FindMyiPhone on your iPhone it will find it.
Your provider can't track a phone without a warrant so having put your own location software like FindMyIphone on your phone would be your only option.
I'm sorry I don't have better news.
More info about Find-My-iPhone: http://www.apple.com/icloud/find-my-iphone.html