If the phone was powered off, it is not easy to track it off! If the thief disabled Internet connection, find my iPhone is not useful at all! The best way is to install an anti-theft app in case your iPhone is stolen/lost. I lost an iPhone 5S, and now installed an anti-theft app like iLostFinder on my iPhone 6Plus. It can prevent the thief from powering off, pulling off SIM card, disabling internet connection and more other anti-theft events. I don't want to post too much like a spam here, guys who need it can view it by yourself. http://ilostfinder.com