stolen

You cannot locate an iPhone with the IMEI or serial number. See this for what to do when your device has been stolen. If your iPhone, iPad, or iPod touch is lost or stolen - Apple Support

If Find My iPhone has been turned off, then you will not be able to track the device, and the thief would have restored the device to use for themselves.

If you have the IMEI Number of the iPhone there is still a chance of locating it.

Did you have a iCloud account on the account? If no then there is no way of finding it via Find My

Tip: You should always have a password these days. It is more secure and makes it easier for you to find your phone when it gets stolen in this case.

Noted.