If you have findmyiphone turned on and the finder / thief have not removed your sim it should show on the map if the iPhone is charged and turned on.
However when O2 disable the sim it will then not work as data is also then turned off.
https://www.apple.com/uk/icloud/find-my-iphone.htmlhttp://support.apple.com/kb/PH2698If your iPhone was on ios7 then the activation lock should stop anyone using your iPhone. Ie putting in their own SIM card.
Also hoping you had pass code lock enabled.
O2 will send you a replacement SIM card. When you receive it remember you need to ring them again to have the lock removed from your account.
Look at any O2 insurance or household insurance or bank account as some give cover too.