Is is very unfortunate that your iPhone was stolen.
"Offline" means that one or more of the following things have occurred on your iPhone:
- The battery has run down
- The phone was powered off by the thief.....(which is the first thing that most iPhone thieves do, so the owner cannot track the phone easily)
- The phone does not have an Internet connection at the present time
Unfortunately, there is not really anything that you can do about this except check a few times each day to see if the status of the phone has changed.
If the phone has a good battery charge, is powered on and has a good Internet connection, the current location of the iPhone will be displayed.
Be very careful if you receive a message that your iPhone has been found. Apple will never send a message like this, so you know that the message is a scam that is trying to trick you into providing information about the phone.