My iPhone 5 got stolen! Is it possible that I might get it back?

As it says on the top, I got my iPhone stolen on Thursday on the train coming home from school. Yeah some idiot snatched it out of my hand while I was going to call my mom. The police made a report and stuff. They said its been going on since Monday. They said that we shouldnt disconnect the phone's service because that way, the police can track it down if the dude who stole it, sells it ilegally.

I'm kinda relieved that its a possiblity they can track it but here are the two big questions.

1. If the dude who stole my phone sells it to an ilegal phone service, can the phone service activate my phone for a customer even if it still has my phone number and service? Is it possible?

2. Since I never knew of the Find My iPhone app, can I still intall it on my computer to my iphone? (I'm an Apple Newbie I don't know)

And again, Is there any way I can get my iPhone 5 back please?

If you didn't have on your settings privacy>gps find my phone on then it would be harder to find. You don't need find your phone app to find it.

Honestly i've had a lot of phones stolen at my cellphone store and the police never caught the guys or found the phones. So if i were you i wouldn't get my hopes up. Sorry