Find my apple watch

By turning off the Apple Watch it is disconnected with wifi , if a person who founds the watch turn it as on then see this article https://support.apple.com/en-in/HT207024

If the device is turned off, you'll need to look for it the old-fashioned way: Start at the last place you remember having it and retrace your steps. Look under the sofa cushions, under car seats, in the pockets of the clothes you wore yesterday.