If it's stolen. They've either broken it down and sold the parts or they're keeping it offline. In order to use your sim in another phone to start resetting passwords linked to your number. Gain access to your Apple ID, look for passwords and accounts and so forth.
The best thing you can do. Is to deauthorize the phone from of your iCloud account. Report your sim lost or stolen. So, it gets deactivated. Change all your passwords. Then get a new sim card.
It's unlikely you'll ever find the phone if someone knows enough to take it offline after stealing it. Now your goal should be to protect all your accounts, personal information, finances and data.