I know who stole my iPhone 5. How do I get it back?

My first time going to this YMCA, and I went to go hide my phone because this YMCA has no lockable lockers.(they have lockers but you have to buy a lock) yeah I get that it was stupid to hide my phone in a gym. But I did it anyways. I made sure no one was looking. Then later I go check and GONE. Right after, I asked if anyone saw who took it. We know who did but he left. So I was PISSED. They said he was sitting down against a wall. And got a glimpse at the iPhone and snatched it.

I went to the front desk to file a report. I used find my iPhone but it was offline. ( thief turned phone off ) I filed a police report, gave them my serial number for the phone and the phone number. I went home tracked it again and it said it was turned on at an address. (I was gaining confidence) then went to the the house with the cop to find out the house was vacant. F. UC.K. I was so pissed. The guy who took it probably went there turned it on at that house that was for rent.

So yeah we know who took it and when i see him at Y what should I tell him? (Btw he's 6'4 and strong, and a pothead)

Also if he sold it how could we prove?

And if the consumer try's putting the phone on a network will it be denied?(since I turned in the serial number to the police)

PS I have two witnesses
Could I take him to court.
How could I prove?

Sry if this didn't make sense it's late and I'm very mad. Worst birthday of my life. Btw I'm 16

AND IT WAS MY BIRTHDAY THE DAY BEFORE THIS All HAPPENED. F. M.L

Added (1). Cruel world and this is one of the first times someone has stolen something this expensive from me (650$). TBH, I've never stolen anything or put down someone in a harsh case. This sub question has nothing to do with the ones above, … But, do you think this world is coming to an end? As a strong Christian I'm questioning God why all this horror is happening in this world? (9/11, Boston bombing, Columbine, Sandy Hook, and many more) I'm starting to loose faith.

My family told me it used to not be this violent 30-40 years ago. Is that True?

Yeah I've recently read a report about this incident. More people are getting phones stolen and some where posting here for help, even people who found phones. Usually when someone has a stolen phone they sale it and it sometimes end up on the other side of the world (even Steve Jobs had the problem). I'm a BlackBerry Z10 user and on my phone there's a tracker that allows me to find it and turn it off to keep the thief from using it and if I wanted to I could turn it back on and wipe all info and track it down. I'm not sure if iPhone has anything similar but all you can do is keep track of it but keep using that site. If he did sale and you have photo evidence or video evidence then they can arrest him and take him in. I know you know who but you need evidence to back up your claim. Oh and yes I believe it is. I'm Baptist and have another belief system but i didn't believe in the whole 2012 thing. I knew it wouldn't then but everything in the book of revelation is currently hopping (the war and the 9/11 were predicted in the Bible).

Ya take him to court. Btw just because your phone was stolen doesn't mean the world is coming to an end lmao selfish