i removed my stolen iphone 4s from the list of devices my account manages is there anyway to reinstate it?

My iPhone 4S was stolen, i do not have find my iphone as an app on it. Fearing that the thief could somehow access my Apple account with my details, I removed it from the list of the devices I managed. However my brother with his find my iphone could still see it on his screen the day after I removed it, it was offline the whole time. The next morning it's gone from the screen. Is it because the removal has been activated? If so, is there anyway I can reinstate it?