Stolen iphone 4s

My iphone 4s has been stolen. I decided to go on icloud and track it as i do have the find my iphone notification on as well as location on maps. when i log on to icloud and click the find my iphone icon, it says no device, can this be because my iphone's battery is dead? the iphone is switched off? or my career has blacked my iphone? PLEASE HELP