Backpacker Gareth Huntley, who is on a sabbatical from his job in the City, 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, last 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 UK Government has stepped up attempts to find the 34-year-old accountant, who is originally from the Leeds-Bradford border, while Defence Secretary Philip Hammond has been assured that "all available search assets" are being used to find him.
Mr Huntley's younger brother Mark 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."
Mr Huntley's girlfriend Kit Natariga has now arrived on the island, while his mother, Janet Southwell, has arrived in Singapore from England and will head to the island at first light.
Ms Natariga said efforts to find Mr Huntley were a tonic to the anxiety, but admitted time to find him was "run-ning 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 backpacker and adventurer who would take utmost care in ensuring he was properly prepared for excursions.