Using Find My iPhone on a strangers phone

My friend lost his phone while out the other night, and we used a strangers phone to use Find My IPhone. We found it. But we are concearned about how long the stranger can see the location of my friends phone. Is there any way for it to sign out my friends account on the strangers phone? Or is he vulnerable to being location stalked by this stranger? Does find my iPhone sign the Apple ID out after a certain time? Will my friends phone still appear on the devices within the find my iPhone app?