Posters of missing and injured people cover Thai hospital walls

The Dutchman was one among thousands of people trying to trace family and friends after a disaster which claimed tens of thousands of lives.

Shattered communications only added to the difficulty of getting news.

But a posting by a stranger on the BBC News website led Mr Delissen to his relatives, who had all survived.

Thank you Voi-Ping. Your message on this site got me in contact with your daughter on Koh Racha Yai. My brother Theo and his wife and daughter seem to be ok, with everybody else on the island. Thank you BBC, thank you internet Rob Delissen, the Netherlands

Mr Delissen, from Nieuwegein, knew the three were holidaying in Thailand on their way to start a new life in New Zealand, but he did not know where.

He turned detective, working out what resort they were staying at by examining pictures saved in his computer's memory cache, but was unable to get through by phone.

Then he spotted a message on the BBC News website from a Swedish man who had contacted his daughter on the same island, Koh Racha Yai, about 30 miles south of Phuket.

Having tracked down the man's phone number in Stockholm, Mr Delissen called him.

"He gave me his daughter's mobile number and I spoke to her," he said.

"Apparently they had been fleeing from the water uphill and everybody was gathered there because there wasn't much high ground."

Mr Delissen said Theo had urged his wife Uta to take their child Lisa to high ground after the first giant wave crashed on to shore, while he went out in a boat to help divers and snorkellers to safety.