How can I use Find My to locate my lost Apple Watch SE?

My son lost his Apple Watch a few days ago and the battery was dead at the time he lost it- it does have cellular service- not sure if that matters at all- as soon as I was made aware that he had lost it, I checked the “find my”app but the watch location was not coming up at all. I reported it as lost and for the past several days it just says “pending.”

My question is, since there was a day or two between when it was lost and reported, could someone have found and changed it or erased it since “find my” was not active right away? The watch is passcode protected. Are they that easy to hack? Also wondering Is there anything else I can do other than activating the find my app and retracing steps?

Thanks!

[Re-Titled by Moderator]