The boy is believed to come from the local area and has not yet been named. He is said to have been in the sea just after 4pm this afternoon with a friend when he disappeared.
Sussex Police began searching their area assisted by the local coastguard and other emergency services around the West Beach area of Newhaven.
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An inquest is due to open into the deaths of five friends who drowned during a day trip to Camber Sands in East Sussex last summer.
Philippa has Monday's weather for the east
Philippa has Monday's weather for the west