Police believe a former professional surfer who went missing on the Thai Full Moon Party island could have been murdered.

Father-of-three Daniel dos Santos, 51, from Portugal, was last seen being dropped off by his wife near a hotel on Koh Phangan on November 16.

Bizarrely, his possessions - including black magic amulets - were found arranged 'in a ritualistic way' in a shop car park on Friday, November 22. There was also a motorcycle helmet next to them which the family said did not belong to him.

Officers are now trying to retrace the footsteps of the surfer, who previously had contracts with Vans and Quicksilver and worked at London's Natural History Museum.

Police Major Chinnakrit Sawaddiwong said: 'The man's friends and family have contacted us. They believe that one situation is that he was murdered. We are investigating that but we do not have any suspects.'

The officer said a report had been filed six days after the initial disappearance. He said there had not been any sightings or any clues to the surfer's whereabouts.

He added: 'The missing man's wife made the report that he was missing. This was six days after she last saw him. His belongings were also found six days after the last contact with him.

'There has not been contact with him since he disappeared. We have interviewed residents and we are in the process of checking CCTV.'

Danie's wife, Avalon, from New York, has two children, Sky, 2, and Ocean, 8, with Daniel. They moved to the island together around a year ago. She has also been searching round-the-clock for him since his disappearance.

The family said they traced Daniel's Apple AirTag and found a bag, swimming flippers, wallet, passport and a clutch bag containing gold and witchcraft amulets placed under a piece of plywood in a Homepro store car park.

There was also a motorcycle helmet - that the family believed belonged to a mystery person - attached to one of the bags.

Avalon said: 'I won't stop until we have found out what has happened. I've been working round-the-clock searching. For sure, there are dangerous people on the islands here and he might have been on the wrong side of someone.'

The wife believes that Daniel did not drown or get lost in the island's jungle.

She added: 'Daniel didn't have a motorcycle or a helmet. But we found someone else's motorcycle helmet attached to his bag. I don't know who that belongs to, or if they're trying to send us a message.

'The bags contained valuables, gold, and Buddhist relics that Daniel had collected from around the world. There's no way the items could be left in a car park for a week without someone finding them and selling them.

'We think someone left them there recently.'

Avalon said Daniel has always been a strong swimmer who 'might have gone into the ocean for a swim to clear his head'.

However, the athlete was an accomplished diver and open-sea swimmer - capable of swimming several miles at a time between islands.

Avalon added: 'I don't know if he went for a swim, went walking in the forest, or someone has kidnapped him, or what.

'He just disappeared without a trace. Nobody on the island has seen him. There has been no bank account activity, no email. We tracked his Air Tag and that took us to his belongings.

'A documentary with a film crew from Portugal had been working with him a couple of weeks ago to make a movie about his career. They were coming back in December to finish the second part. He had a lot going on, he was in good spirits, so it doesn't make any sense. 

'Daniel was a routine person. He was stable, and always on a schedule. He made our children follow a routine and gave them stability. 

He could swim across the ocean between islands. He could dive 42 metres deep. He was at home in the ocean. He was familiar to the big waves of Portugal, so the water in Thailand was nothing to him, it's so still. I could never imagine him drowning. 

'Daniel has PHDs, speaks different languages. He worked at the Natural History Museum in London, he was incredibly intelligent and in excellent health.'

The Full Moon Party is a well-known monthly event held on Haad Rin Beach in Koh Phangan. It is celebrated on the night of the full moon, attracting thousands of party-goers from around the world.