A Malaysian police team has arrived on a jungle-covered island to search for a charity volunteer from London who has been missing for four days.
Gareth Huntley, from Cricklewood, disappeared on Tuesday after embarking on a trek in Tioman Island.
A team of up to 30 people and one dog arrived on Saturday to try and find him, locals have told his family.
His mother Janet Southwell, told the BBC she thought the police effort to find him had been slow.
His brother Mark, who lives in Leeds, told BBC 5 live's Stephen Nolan programme that for days it had only been local people and Gareth's friends who were searching for him.
He added he wanted British authorities to "put more pressure on the Malaysian police force and search and rescue to do more to intensify the search".
He said his 34-year-old brother's disappearance was out of character and he would normally be good at keeping in touch.
"For him to not turn up and still be missing at this point - he is not like that, he would have made contact by now," he added.
His parents are due to fly out to Malaysia later and they hope to arrive at the scene by Monday.
It is feared he either broke his leg and was unable to get help or he was bitten by a snake.
Ms Southwell, from Bradford, said: "He was having a lovely time. He was due to start a new job next week in Singapore, life was very positive and he decided to have one last week's break before going back to Singapore to commence his new life."
She said he should have been back from his trek within two hours and he was carrying water and wearing proper footwear. He had a phone but there is no signal in the area.
She added: "At this stage I feel it is essential that the search be intensified as time is running out for Gareth, so I would really appreciate the support of the Malaysian authorities and the UK government with this."
Mr Huntley's friend Hannah Alice Grant, who is on the island, wrote in a detailed account on Facebook of the search, that the police were seen "swimming and messing around in the waterfall" instead of searching for him.
His friend Sophie Wilson said a British Army commander, who had lived on the island and knows the topography well, told them that it was impossible to get lost because all the mountains and valleys lead down to the sea.
She said the search had been hindered by a lack of dogs or heat-sensing equipment.
"Clearly he's lost but it's not complicated, it's a small area; we just need people to penetrate that dense jungle," she said.
Mr Huntley had been working at the Juara Turtle Project. Fellow volunteer Charles Fisher said a group had gone to search for him after he did not return from the "huge wilderness".
He said the group had checked various routes to the waterfall, 6km (3.7 miles) away, while a further search the next day had also proved fruitless.
A spokeswoman for the Foreign Office said: "We are aware that a British national has been reported missing in Malaysia since 27 May.
"We are providing consular assistance to the family and are liaising closely with the local authorities."