Jamie Taggart, 40, who runs the Linn Botanic Gardens in Dunbartonshire, was last seen on the morning of October 31 heading towards the Sapa mountain range to search for rare botanical specimens.
He had told people at the guest house where he was staying that he intended to be back that night or the following morning, but has not been seen since.
An initial five-day search of the area involving 10 people failed to find any trace of him and had to be suspended due to poor weather and an injury to one of the searchers, who suffered a broken ankle. Police have also carried out a search of villages in the area.
Phil Hoolihan, of Ethos Travel in Sapa, a British ex-pat who is helping co-ordinate the search, is today expected to meet national park authorities to obtain permission to search the area more extensively, covering a distance of more than two days from where Taggart was dropped off.
The plan is to search three routes that he may have taken - from Tram Ton to Cong Troi (Heaven Gate), Lai Chau and Khoang Village, which will take four to five days.
An appeal has been launched to raise money to cover the costs of the search, which are estimated at between £1600 to £2000.
New pictures have also been released that show Taggart in Vietnam during his last trip there in 2011.
The gardens run by Taggart were founded by his 82-year-old father Dr Jim Taggart, one of the most prominent botanists in Scotland.
Ian Sinclair, who has known Jamie Taggart for 25 years and spoke to him the night before he left Scotland, said the priority would be searching gullies and gorges.
He added it was hoped the search party would involve 20 to 25 local men, forest rangers and volunteers.
"We are basically doing our utmost to bring Jamie back," he said. "There are an awful lot of folk who care for him, his father and their garden."
The "missing" posters, which are being distributed in the local area this weekend, show a picture of 40-year-old Taggart, stating his full name, James Henry Ker Taggart, and that he checked into the Ngoc Anh Guest House in Sapa town on October 30.
It adds: "He left the guest house on the morning of 31 October 2013 via a motorcycle taxi and proceeded to Tram Ton area of the Sapa mountain range.
"James was last seen proceeding in a westerly direction into the mountains. James is a botanist and specialises in the discovery of new species of mountain plants."
It is believed Taggart may have been looking to study and photograph plants at greater altitude than he had explored before.
His passport and rucksack were left behind at the guesthouse.
The area is not considered dangerous for travellers and it is thought local people would have sheltered the botanist had they found him in distress.
But concerns are growing for his welfare, with the dense temperate rainforest described as difficult terrain and "torrential" rainy conditions over the past few days.
Jim Taggart bought the Linn Villa in 1971 and set up the famous garden by sourcing plants from China, Peru and the Himalayas.
He only found out his son was missing when he failed to appear on a flight home to Scotland on November 29.
In an interview last week he said: "I had four text messages from him then his mobile phone went dead His last text message said exactly where he was going.
"He was on his own but had been in that part of Vietnam two years previously and knew his way around.
"I don't think he got lost. Either something happened on his first day on the hills or there is some explanation we can only guess at."
Jamie Taggart, a retained firefighter who is single, took over the gardens in 1997. They feature on Historic Scotland's list of nationally important gardens and designed landscapes.
l Contributions towards the cost of the search for Jamie Taggart can be made by a cheque made out to "Friends of the Linn" with the words "for Jamie" written on the back. Cheques should be sent to Mrs Rie Bellamy, Treasurer, Friends of the Linn, Portkil House, Kilcreggan, Helensburgh, G84 0LF
Contributions may also be made through the Friends of the Linn bank account at Bank of Scotland, Helensburgh Branch, sort code 800831, account no 00704064. The words "for Jamie" should be used.