IPhone was stolen and I have find my iPhone app

So yesterday I got my iPhone 5 stolen. I had the app find my iPhone on it. I tracked it down for about half an hour but then I think the guy turned it off. It's been 24 hours now and now the iPhone on the app say "offline". The ind y iPhone app will notify me as soon as the location changes, so does this mean that the phone is still turned off? I already locked it and called my provider. They also locked it and if they try to put it into another provider it will appear that the phone was stolen and they can't use it at all. If thy reset my iPhone they will have to turn it on and then I can track it down right? If they reset it, will my iPhone still appear on the find my iPhone app or will it disappear? How would I know if they resetted my phone?