Nathan Wood was last seen near the River Dart in Totnes, Devon, on Friday evening in a "distressed state", officers said.
It was feared he had fallen into the river after taking a so-called "new psychoactive substance" (NPS).
Deep water divers were drafted in on Sunday to help in the search for Mr Wood.
Search teams recovered a body earlier which would "appear to be a male of the right age range", a spokesman said.
The body has not been formally identified, but Mr Wood's family have been informed.
Inspector Tracey Sharam, from Devon and Cornwall Police,  said: "We'd like to thank everybody for their help and support that have turned up over the last couple of days helping us with those searches.
"Our thoughts at this time are with his family, his friends and the community in Totnes."
Police said the teenager had been out with a group of friends on Friday night and believed he entered the water at about 18:30 BST.
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".
The Dartmoor Rescue Group and a helicopter helped in the search efforts over the weekend.
Mr Wood's friends confirmed to officers the teenager had taken a drug on the night he went missing.
New psychoactive substances, formerly known as "legal highs", are synthetic versions of drugs such as amphetamines and cannabis designed to mimic their effects.
A body has been found by police searching a river for a missing 16-year-old boy.