Dr Mosley had been on the beach with another couple but had left his phone there before he set off for Pedi, a tiny hamlet a mile away where he had been staying, at around 1.30pm.
Constantina Dimoglidou, a senior police spokesman, said: “Any and every attempt to track him down has not produced any result. We have now asked the fire brigade to assist in the operation in the case that he may have slipped, tripped, fallen, even [been] bitten by a snake, remaining injured somewhere.
“There is just no trace of him – none whatsoever, and that means that, for us at least, every potential scenario is open and being investigated.”
Four police officers, eight firefighters with a drone and eight volunteers are participating in the search.
Police have also requested the deployment of a police dog and a helicopter from the civil protection authorities.
The area where the presenter went missing is considered “difficult as it is quite rocky”, Lefteris Papakalodoukas, the Symi mayor, told Kathimerini, the Greek daily newspaper.
Papakalodoukas described the heat on the island on Wednesday as “unbearable” and said “one could easily faint in such conditions”.
An excessive heat warning was issued by the Hellenic National Meteorological Service on the day Dr Mosley went missing, with temperatures reaching 36 degrees.
Papakalodoukas said Dr Mosley “wanted to walk back from the beach, but that’s a distance of about an hour and a half and there are shortcuts he may have taken”.
Adriana Shum, a British expat and local journalist who has lived on the island for 30 years, said on Thursday morning: “A search and rescue team is coming from Athens with drones and other more sophisticated equipment to extend the search.”
She shared a recent photo of Dr Mosley on the island to the Facebook group Friends of Symi, writing: “Have you seen this man. He set off to walk back from St Nick’s at about 13.30 and failed to make it home.
“His friends are concerned as it is six hours since they last saw him. His name is Dr Mike Mosley and he is a familiar face for many British people as he has appeared on the BBC.
“The police and coastguard have been informed. EDOK, the island’s rescue team, is also involved. So far, he still has not been found and the search continues.”
Another expat wrote on the Facebook page: “Be assured that Symi is a very resourceful island. The authorities and volunteers are doing everything possible to find this man. You will be notified just as soon as there is news.
“And as an aside, it really is of no consequence as to how famous or successful this chap is, or that he is a celebrity. The efforts to find him are exactly the same as for anyone else here on Symi.”
Colleagues and friends of Dr Mosley expressed messages of support for his family.
The television presenter Jeremy Vine, who has featured Dr Mosley on his BBC Radio 2 programme, said: “I’m praying this lovely man is found and thinking of Claire and the whole Mosley family.”
Tom Watson, the former deputy Labour leader who credited his own 50kg weight loss to Dr Mosley’s advice on fasting, said: “My thoughts are with the family of Michael Mosley who has gone missing.
“He is a hero to me, and I hope he is found safe.”
Martin Lewis, the financial journalist and broadcaster, tweeted that he was “disturbed” to hear the father-of-four is missing.
“I hope he’s okay,” he said.
Dr Mosley fronted the Channel 4 show Michael Mosley: Who Made Britain Fat and was part of the BBC series Trust Me, I’m A Doctor.
His show Lose A Stone In 21 Days With Michael Mosley is currently streaming on ThreeNow.
He also appeared on the Herald podcast The Little Things in April.
Saleyha Ahsan, his co-star on Trust Me I’m A Doctor, said the news was “shocking” and that she was hoping Dr Mosley would be “found safe”.
“I literally feel sick with worry,” Ahsan added.
“Don’t even know what to say.”
