The local lad was spotted by a canoeist just outside the town yesterday. He was reported to be heading towards the water in a “tripping and excited state”, according to police.
Cops said they feared he had taken a banned ‘new psychoactive substance’ – formerly known as a legal high drug.
Speaking last night, acting Sgt Kevin Rowe said: “There was a possibility he may have taken some sort of [formerly] legal high which has had an adverse effect on his behaviour and caused him to behave quite irrationally.”
Rescue teams searched the river through the night and into the morning after Nathan was reported missing by pals.
But efforts have now been stepped up after cops found a pile of clothes belonging to the missing teen.