Dr Jim Taggart only found out through an email sent to a family friend that the Foreign and Commonwealth Office was treating the search for his son Jamie as officially abandoned.
But Mr Taggart had been in contact with the local authorities in the north Vietnam region, which provided him with a timetable for an official search this month.
The next review of the official search for the 42-year-old is due around the start of next week. It is being conducted in tandem with a privately funded search involving local trackers paid for by donations to a search campaign.
Mr Taggart, of Cove, Argyll and Bute, left his boarding house in the town of Sa Pa to search for rare plants on November 1 but did not return from the trip in the northern mountainous region.
In an email to the family, a UK Government representative said the official search by local authorities had been suspended.
The Foreign and Commonwealth Office note said: "My colleagues in the British Embassy in Hanoi have today spoken to the Ministry of Foreign Affairs (MFA) concerning the local authorities within the Sa Pa region looking for James.
"The MFA has been notified by the local authorities that, as it has been nearly three months since James went missing and there have been no clues found to his location or sightings of him since October 31, they have suspended the search. I am sorry this news is likely to be distressing to you and James's friends as it continues to be everyone's hope that clues to James's location will be found.
"The MFA have agreed that, should they be contacted by the Sapa local authorities in the future with any information with regards to James, they will notify the British Embassy in Hanoi who will in turn arrange for you to be notified via the Foreign and Commonwealth Office."
Mr Taggart runs Linn Botanic Garden in Cove, which his father founded. He planned to document high altitude plant specimens and it is thought he went missing somewhere in or around the Hoang Lien National Park.
He may have taken public transport in the direction of Lai Chai Province, and searches have been conducted in the Ban Khoang Mountain.
A series of sightings in four locations have been confirmed in recent weeks by searchers but all date to the day he went missing.
Mr Taggart said: "I am in touch with Luong Van Hao at the national park and that (the suspension) is not what is happening.
"The search was resuming on February 5 and was due to take two weeks to cover the area over the mountain."
The missing man was last seen on the main Sa Pa Town road heading west before it forks and at one stage was trying to obtain a permit to the national park.
Mr Taggart said: "There were no more sightings of him on either of the two tracks so the conclusion is he must have gone up the mountain either to the left or right."
He said he believed it unlikely he would have survived but added: "If he's not found then what happens?"
An FCO spokesman said it had been notified by local government authorities the search had ceased but said: "We continue to provide consular assistance to the family at this difficult time."