BBC News - Teenage boy 'swept away' by sea in Newhaven
Sussex Police received a call at 16:15 GMT to say the boy, who had been swimming with a friend off West Beach in Newhaven, had been "swept away by the current".
The Newhaven Lifeboat team said at 21:45 GMT all teams searching off the coast had been stood down.
In a tweet, it said its thoughts "go to the boy's family and friends at this sad time".
The boy was last seen playing in the surf about 10m offshore, the Maritime and Coastguard Agency said.
Earlier, a spokeswoman had said weather conditions at the scene were very bad.
"The weather conditions are just atrocious, with poor visibility making it extremely difficult," she said.
She explained that police were with the boy's family and they were "distraught".
A police spokesman said it was a "very distressing incident".
He added: "All agencies remind people of the dangers of being at seashores in adverse weather, especially in view of the approaching severe weather conditions overnight.
"The advice is straightforward - stay clear."