As a mum of a bolter, I feel this so deeply and am praying for him to be found.
It is amazing how far they can run, they just keep on going. I feel that maybe he has gone a good few miles... possibly even 7 or 8 miles by now and is outside of the original search area.
I think the fact he hasn't been seen is because he has gone into the fields and woods rather than around the houses. He is hemmed in by the A road to the north and the river to the west and south. So assuming he stays out of the river, he's in the woods and fields somewhere within the immediate mile or two, or further away to the east. You'd imagine if he had got to the A road he would have been spotted (hopefully).
He will be hiding as he'll be scared of people or or being told off. Hes probably under a hedge or in a little gap somewhere. But he'll be very hungry by now.
My advice to the volunteers searching would be gently calling out... "We have some chocolate for Noah"... or whatever his favourite food is. Or saying in a happy tone 'Noah has won the game and now he can come and get some chocolate!" I realise I sound bat shit crazy but there are mums of autistic bolters among us that I'm sure will know what I'm talking about.
So not calling out his name directly, but mentioning his name indirectly and putting the focus on food, and making it sound fun.
I think not calling out at all would be a mistake. I'd call out things like "mummy is here to take you home and she has some yummy food for you". He needs to feel like he's not in trouble, it's safe and that there's something in it for him, a reward of some sort.
I hope someone in the search reads this.
Praying for you Noah, and all the family.