Dr Michael Mosley is believed to have gone missing on a Greek island.
The 67-year-old is known for his appearances on television programmes including This Morning and The One Show.
He is also credited for the increasing popularity of the 5:2 diet for losing weight, which involves fasting for two days per week.
Representatives for Dr Mosley confirmed a search was ongoing for him, telling the Mirror that they were “very worried about him".
A post on a local Facebook group in Greece said rescue teams from Athens were heading for the island.
The appeal read: "A search and rescue team is coming from Athens with drones and other more sophisticated equipment to extend the search.
"They are expected to arrive by about 1pm."
The post continued: "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 6 hours since they last saw him.
"His name is Dr Mike Mosley and he is a familiar face for many British people."
The 67-year-old broadcaster did the Channel 4 show Michael Mosley: Who Made Britain Fat? and was part of the BBC series Trust Me, I’m A Doctor.
He also lived with tapeworms in his guts for six weeks for the documentary Infested! Living With Parasites on BBC Four.
Mosley has been given an Emmy nod for BBC science documentary The Human Face, presented by John Cleese and featuring a raft of human faces including Elizabeth Hurley, Pierce Brosnan and David Attenborough.
He also advocated for intermittent fasting through the 5:2 diet and The Fast 800 diet.
Mosley has three children with his wife Clare Bailey Mosley, also a doctor, author and health columnist.
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