To play devils advocate here, if someone 'lost' that snake and really was concerned, i would imagine they would be checking all the places that the OP already let know. And if it was the person who moved and they were worried, I'm sure they would have contacted the neighbors asking. I mean how do you 'lose' your snake and not notice it until after you have moved lol. I check on my gang every morning i wake up so i would know right away if one was missing.
Honestly, it is not the OPs responsibility to go out searching for the owner It is is the owners responsibility. On the flip side, the OP should not try and conceal the fact he found the snake which to me it sounds like he isnt as he posted on FB(im guessing the local reptile club there) and has let animal control and whatever other 'lost and found' there is for pets in his area.
Also to the OP, if someone claims it, make sure they show some kind of proof like a receipt from the breeder or contact info so you can call the breeder and actually ask the breeder is 'Joe' actually bought a snake from him as that retic does look young so I'm sure whoever sold it would remember. Any Joe can just say "Oh you found my lost retic. Im so glad, Can I have him back". When in reality, that isnt his real owner and the guy just saw you post a lost and found retic and he wants to claim it to keep or sell.