Traveller Gareth Huntley, who is originally from the Leeds-Bradford border area, has not been seen since he went on a trek to visit a waterfall in Tioman Island, off the south eastern coast of the country’s mainland, on Tuesday morning.
He told friends at the headquarters of a nearby charity project where he was volunteering that he would return by 2pm the same day but failed to come back.
The trek to the waterfall reportedly involves slippery, poorly marked paths surrounded by dense jungle.
The obvious dangers are getting lost, falling or being bitten by a snake.
His family fear he may have got lost or been hurt and have raised concerns about the rescue effort, saying police did not initially join the search.
The British Government has stepped up attempts to find the 34-year-old, who is on sabbatical leave from work, while Defence Secretary Philip Hammond has been assured that “all available search assets” are being used to find the trained accountant.
Mr Huntley’s girlfriend Kit Natariga has now arrived on the island, while his mother, Janet Southwell, from Bradford, has arrived in Singapore from England and is due on the island today.
Ms Natariga said efforts to find Mr Huntley were a tonic but she admitted time to find him was “running out”.
She said: “It’s really tough coming onto the island, we’re in a bit of a helpless state.
“We cannot give up...time is running out.”
She said her boyfriend was an experienced adventurer who would take utmost care in ensuring he was prepared for excursions.
Mr Huntley’s younger brother, Mark, 30, from Leeds, said the family were keeping positive as a result of efforts to find him.
He said: “We want to personally thank David Cameron and Philip Hammond for their reassurances. It is a very big positive for us.
“We are, of course, very grateful to the Malaysian people and the authorities for their work too. Everyone has been fantastic.
“We are told that local people went out to look for Gareth as soon as he was first described as missing - so without them there would not be a search mission. What we need now is for that work to continue and to find my brother.”
Mr Huntley’s mother said “real help” was needed to find her son, who is an accountant.
In an appeal to the Prime Minister, she said: “We need boots on the ground, search teams and dogs so that we can bring our son back alive. As our Prime Minister I write to you but as a mother too, I hope you’ll help me.”
A Foreign Office spokesman said: “The Defence Secretary, who is in Malaysia, has spoken to the Malaysian Defence Minister this morning to confirm that all available search assets are used to find Gareth Huntley.
“He was assured that the Malaysian authorities would do all they could to locate him and had already deployed significant assets including dogs, boats and a helicopter.”