Fears were growing for the multi-millionaire head of the US-based sports giant Quiksilver last night after his empty speedboat was found upturned on a French beach.

Pierre Agnès, 54, was last seen setting out in rough seas at 7.30am on Tuesday. The French father of three is believed to have been alone on board the 11-metre ‘Mascaret III’ when it headed out in the Atlantic near the resort of Biarritz on the south-western coast of France.

He was planning to go fishing near Capbreton, at the mouth of the Boudigau and Bourret rivers. In a call to French maritime authorities soon after setting out, he said he was delaying his return because of thick fog.

The alarm was raised at 9.15 am after friends and family said they had been unable to reach him. Soon afterwards, the Mascaret III was found empty in Soorts-Hossegor, a well-known surfing beach about 15 miles north of Biarritz.

It appeared to have washed up. Two boats and three helicopters were scrambled to search for him and he was officially listed as “missing at sea”.