Find my iphone is kinda a joke. You can easily turn it off or wipe the phone. That's why the ops phone is no longer showing up on find my iphone but he can still call it. You can remotely wipe it but the theif is just gunna pop out the sim and wipe it and sell it or re register it. Or if you we're running a pword he prob wiped the phone but it auto reactivated your sim that was still in it. If its any consolation hell never be able to get it factory unlocked, he'll either be tied to your carrier or tied to a jailbreak. Cancel that sim and get a new phone. You need to remote wipe immediately, he can jailbreak it and hell be able to open ios with no pword, or he can use a computer program to rip the pword from the phone without even jail breaking it.
As far as getting imei blacklisted, it doesn't really work that way. The policies vary from carrier to carrier. It's not industry wide. Verizon is the only carrier I know for a fact even lets you blacklist a imei as stolen. Problem is you get your phone blacklisted on AT&T then the perp just activated it on tmobile or sprint cause the blacklist is not industry wide. Not sure how it works with virtual carrier, like if AT&T blocks an imei then the block carries down to the virtual carriers under them.
The cell phone industry is actually trying to iron out a better plan for dealing with phones reported stolen as we speak. I don't understand why apple can't set it up so you can register a phone on their end and it just gets tracked forever, so you can't just turn off the tracking on the phone or wipe it. Apple has the ability track phones like this but they don't have this option open to the public.
I know why the phone industry doesn't want this ability open to the public though, it'll just cost them money and headaches. People will forget to untracked or unblock a phone when they sell it, then the new owner will be all pissed when they can't use the phone they just bought anonymously on cl. It already is a big pain with activating. Also the darker side of this is that apple LOVES the fact that the iPhone so highly targeted for theft, it makes people lose their phones and have to buy new ones. If they had an industry wide blacklist for stolen phones then not only would it cost them money to run the blacklist but it would cost them money in lost sales of phones to replace the stolen ones, they see it as a double blow to the bottom line.