The Foreign and Commonwealth Office has written to the Vietnamese Ministry of Foreign Affairs to raise the profile of the disappearance of Jamie Taggart 42, who runs the world-renowned Linn Botanic Gardens at Cove, Argyll and Bute.
He went missing after going trekking in October last year, two days into a plant-documenting trip.
The official search was called off in March but Mr Taggart's family and friends have raised thousands of pounds to fund continued searches and local investigations.
First Minister Alex Salmond and Greens co-convenor Patrick Harvie are among those to have backed moves to maintain pressure on keeping the hunt going.
Now Hugo Swire MP, Minister of State at the Foreign Office responsible for consular matters in Vietnam, has written to supporters of the campaign saying he has urged Vietnamese authorities to ask police to look at the case again.
He said: "I wrote to Vice Minister Bui Thanh Son, my counterpart at the Vietnamese Ministry of Foreign Affairs, to urge the Vietnamese Government to maintain the profile of Mr Taggart's disappearance locally and ask that the police review their investigation for new leads that might warrant further searches.
"We now await their response to consider whether there is any further support we can offer.
"FCO consular officers will continue to be in contact with Mr Taggart's parents to provide consular assistance to them both during this extraordinarily difficult time."
He also said: "This obviously must remain a very distressing time for Mr Taggart's family.
"Sadly there is still no evidence as to the direction he took when he went trekking, but I am pleased that the searches are continuing.
"Our Embassy in Hanoi continues to liaise with relevant authorities and they have agreed to update us."
Mr Taggart's mother Jill Mary has said she believes her son is alive and could be in prison.
The gardens at Cove run by Mr Taggart were founded by his 82-year-old father Dr Jim Taggart, one of the most prominent botanists in Scotland.