From Google Earth, if he went down what looks like the foot path/bridle path to the pond as reported, it seems to be a long relatively straight open path of around 200 metres off road. I find it strange someone who was looking for him wouldn't have immediately spotted him running down it even from a distance unless there was quite a delay in noticing he was gone but then how would they know what direction he'd gone in?
I can't see anything that looks like an alley from the playground, just that footpath.
Really hope he's found safe and well, although that's looking increasingly unlikely almost 12 hours later unless by sheer miracle he's found on someone's property. There are houses along there but they would have been the first ones to have been asked to search gardens/garages surely.
Please don't let this be another Mikaeel Kular. That case haunted me.