The mother of British man Gareth Huntley who has gone missing in the Malaysian jungle has urged David Cameron to "make one phone call" to the country's leader "before time runs out".
Mr Huntley was last seen four days ago on Tioman Island, where he was working as a volunteer for a conservation charity.
The 34-year-old left the charity headquarters to go walking by himself and did not return. His mother Janet Southwell said she is “extremely concerned” about her son’s welfare and has not received any official information on the search for him.
In her letter to the Prime Minister, she appealed to him as a father who knows "that we'd do anything for our children" and asked him to "please do the right thing". She wrote: "Make one phone call to the Malaysian leader to insist that they deploy real help to find Gareth before time runs out. He is out there in the jungle and he needs help."
Ms Southwell and her son's father are planning to fly out today to assist in the search.
A Facebook page set up to find Mr Huntley urged the Malaysian police to "work faster" on Friday.
The post said: "He [Mr Huntley] never returned to the Juara Turtle Sanctuary on Tioman Island where he was staying and volunteering.
"We need to find him ASAP and put pressure on the Malaysian authorities, they seem to be dragging this on without urgency, action and results. It's become very unclear whether the Malaysian authorities understand the urgency of the situation and whether they’re acting fast enough, or prioritising this."
Charles Fisher, a manager at the Juara Turtle Project, said he believed police were now doing the best they could in a situation made difficult by the "wilderness" Mr Huntley failed to return from.
He told The Independent that Mr Huntley had left at noon on 27 May and said he was heading along a popular trekking path to visit a waterfall, in what he expected would be a two hour journey.
Volunteers from the project and locals from the community went to search for him after he did not return, but their efforts proved fruitless.
Mr Fisher said: “This is the wilderness location and I think that the police are doing the best that they can in this situation. They have sent out search parties to go looking for him; they have set up a task force and a search and rescue unit.”
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."