Can phone still be tracked?

If someone finds an iphone, successfully restores it without needing apple id and password, and changes sim cards can the phone still be tracked?
If so can you explain how? If Find My iPhone is turned on wouldn t the person have needed the apple id and passcode before restoring it?

IWorld headphones are connected to my iPhone but I can't hear sound?

The headphones are fully charged so I know that isn't an issue. I've tried restarting my iPhone 6s and the headphones to connect them again. All the functions work, like turning up the volume and changing a song, I just can't hear anything from the headphones. My Bluetooth icon at the top part of my iPhone won't show up gray (showing that something is connected) or show the battery. I have had my phone connected to other Bluetooth devices like speakers and it works fine.