If the watch is dead, it cannot send you its position to help you find it. You will have to search manually. Look thoroughly close to the places where you usually take it off your arm or where it may have slipped off. Someone found the watch among the dirty laundry.
If the watch might have been stolen, report it to the local authorities.
See this page: If your Apple Watch is lost or stolen - Apple Support
If you didn't turn on Find My iPhone before your Apple Watch was lost or stolen and your watch isn't connected to WiFi or your paired iPhone, you can't use it to locate your device. However, you can use these steps to help protect your information:
- Place your Apple Watch in Lost Mode. When your watch is in Lost Mode, your passcode is required before anyone can turn off Find My iPhone, erase your watch, or pair it with another iPhone.
- Change your Apple ID password. When you change your Apple ID password, you can prevent anyone from accessing your iCloud information or from using other services from your missing device.
- Report your lost or stolen device to local law enforcement. Law enforcement might request the serial number of your device. Find your device serial number.
Find My iPhone is the only way that you can track or locate a lost or missing device. If Find My iPhone isn't enabled on your watch before it goes missing, there is no other Apple service that can find, track, or otherwise flag your device for you.