Sussex Police has issued a witness appeal following reports a 28-year-old got into difficulties after entering the sea at Brighton.
A spokesman said officers were contacted just after 7.30am this morning (September 30).
They added: “He had told friends he intended to swim round the pier but they became concerned when he failed to appear.
“The Maritime and Coastguard Agency was informed and took charge of a search operation, which involved deployment of a helicopter, Brighton RNLI inshore lifeboat and the Shoreham coastguard team.
“Police assisted with a shoreline search, but no trace of the man could be found. Shortly after 11am the MCA suspended its operations pending any further information.”
The missing man is described as white, 5’ 1”, of skinny build and with dreadlocked hair and he had stripped off his clothes before going into the water, police said.
Anyone seeing the man or who may have other information is asked to report details online or to phone 101, quoting serial 279 of 30/09.