Gareth Huntley disappeared on Tuesday after embarking on a waterfall trek in Tioman Island.
A group of volunteers and local people have been into the jungle to search for the 34-year-old but have not found him.
His family has called for the search for him to be intensified.
“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,” his brother Mark told BBC 5 live’s Stephen Nolan programme.
A friend, Kyle Neo Kai Fu, told Sky News Sunrise he is certain his friend is alive.
“He knows a lot of things about self-sustainability. I think he’s a survivor.”
Mr Huntley had been working as a volunteer at the Juara Turtle Project.
The Foreign Office is aware he is missing and is offering support.
A Facebook page has been set up to help try and find him.
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