Police were initially called shortly before 2pm on Wednesday to reports Ben Heron, from the Lancaster area, had gone into the water close to the Stork Hotel on Corricks Lane.
A large-scale search, involving coastguard and police helicopters together with search teams on foot, was immediately launched. This resumed first thing on Thursday morning.
Police searched along the coast from Ocean Edge to the Wyre Estuary and up the River Lune as far as the Lancaster Weir, together with colleagues at the Coastguard and Lancashire Fire and Rescue Service.
The search ended at 4pm but unfortunately Ben has not yet been located.
Police are appealing to anybody with information about Ben’s disappearance to contact them.
Inspector Charlie Clay, of Lancaster Police, said: “We know residents will have seen activity in these areas and we would like to thank them for their patience while our search continues.
“We are doing everything we can to locate Ben and would appeal to anybody with information about his disappearance to contact us as soon as possible.”
Ben is described as white, of slim build, around 5ft 7ins tall, with short, fair hair.
He was last seen wearing a thin, black jacket, light blue jeans and dark-coloured trainers.
Anybody with information is asked to contact police on 101, quoting log number 695 of April 26.