Police are searching for the 10th Earl of Shaftesbury who disappeared in the South of France two weeks ago.
French police said the Earl, whose full name is Anthony Ashley-Cooper, arrived in Nice on November 3 by plane.
He was last seen two days later and has made no contact with his family since.
French police yesterday issued an appeal for help to find the 66-year-old through the local newspaper Nice Matin.
A spokesman said today: "He came to France on November 3 by plane and arrived at Nice airport. Since November 5 we have no news and his family also.
"We think he did not take an airplane to go to another town."
He said the Earl had a girlfriend in the nearby town of Grasse, famous as a perfume-making centre.
"Yesterday, in a French newspaper, we put his photograph but we have no news."
He added that the Earl was "a little extraordinary" in that he could get on a plane to another country without telling anyone where he was going.
Police in the City of London and Hove, East Sussex, where the Earl has homes, are helping Nice police with the investigation.
A Sussex Police spokeswoman said they were in regular contact with the Earl's son, also named Anthony, at the family seat in Wimborne, Dorset.
She said: "We are concerned for the Earl's welfare. He went to France on a trip and stayed in the Antives area in Nice.
"Then he was going to move to Cannes for a few days.
"He spoke to his family on November 4 and 5 and was due to return to the UK on November 10 but nobody has seen or heard from him since November 5.
"The family are very concerned because it is out of character and we will continue to remain in touch over the coming days."
She added that he has a mobile phone with him but family and friends have been unable to get through.
The report in Nice Matin states: "For now it's only a worrying disappearance which could rapidly become a criminal affair."
The French newspaper said the disappearance was reported by a female friend. Police were also informed by the Earl's lawyer that he had been the victim of an "agression" or confrontation in Grasse last year, it said.
Investigators are awaiting results of inquiries in England as to whether there have been any transactions from his bank accounts, the report states.
The French newspaper report also compared the disappearance with that of Cannes businessman Christophe Dalmasso, who vanished last year.
Police said there were no sightings of the Earl at his luxury seafront home in Adelaide Crescent, Hove, overnight.
Inspector Beryl Bacon, of Hove Police, said: "This is completely out of character and very worrying for his family and friends.
"I will not be drawn into commenting on any speculations or rumours surrounding his disappearance."
She appealed for anyone with information to come forward.
The Earl is described as 6ft 1in and thin, with thinning grey hair and blue eyes.
He has large, heavy-framed red and pink glasses and normally wears casual clothes and a large watch.
Nice police said they had received no reported sightings of the Earl since the appeal was made in the local newspaper.
The father of two sons, whose interests include mountains music and ecology, was educated at Eton and Christchurch, Oxford.
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