Cayenne,I don't know if you've already done this,but I would go and knock on every door in the neighborhood where he was sighted,check their backyards.
For him to have survived this long in the cold,someone must be feeding him..some people just don't look at posters
As for Animal Control,they must know,an animal can freeze to death just falling asleep in that cold,whether it be a trap or just under a bush....he needs to be found.
Actually,when I was trapping a little stray,Humane Society told me not to leave it out after I've gone to bed and I usually brought it inside after midnight.
I still managed to trap the cat,since it got dark really early
Luckily he was micro-chipped and his owners picked him up,at HS.