If you can’t find your device, use Lost Mode right away to lock it with a passcode, display a custom message on the screen, and keep track of its location. If you can’t use Lost Mode because Find My iPhone wasn’t set up on your lost device, see the Apple Support article If your iPhone, iPad, or iPod touch is lost or stolen.
This worked great. I set the passcode, put a message on the phone with a # to call. Got a call this afternoon and was able to recover my iphone. Real happy and Real Real Lucky that an honest caring person found it read the message and called the number.