The emergency services were alerted to the crash shortly before 9pm. Local gardaí secured the scene while ambulances and fire crews attended from across the county. Despite their efforts, all four men were pronounced dead at the scene.
Forensic collision investigators continued to work at the scene of the crash today, trying to establish the sequence of events before the fatal crash.
The car ended up off the road beside a low bridge at the bottom of a dip in a minor road.
The roof of the vehicle was cut off by the emergency services during the rescue efforts.
As the gravity of the depth of the tragedy spread around the western Donegal communities of Gweedore, Gortahork and Falcarragh, Supt David Kelly of Milford garda station issued an appeal for information on sightings of the car the men were traveling in yesterday.
“Garda last night, at approximately 8.40pm received a report of a single vehicle collision at Gleannhualach. When they attended the scene they found one vehicle, a 01DL registered silver Toyota Corolla hatchback off the road and there were four casualties. Also in attendance were the HSE ambulance service and our colleagues from Donegal County Council fire and rescue service.
"It was dark, it was a tragic scene, family members arrived. I'd like to sincerely on behalf of the Gardai and my other colleagues to offer our condolences to the families, their friends and the community following this tragic incident.
"I would like to make an appeal now to the public and the local community. If anyone saw that silver Toyota Corolla with a 01DL registration travelling in the direction of Magheroarty to Gweedore yesterday evening prior to 8.40pm, or indeed earlier in the day to please contact the Gardai at Milford garda station on 074 9153060 or the garda confidential line 1800 666111."
A local priest who attended the scene last night described the incident as "the stuff of nightmares".
Fr Brian O'Fearraigh, from the parish of Gweedore, said he received a call to attend the scene at approximately 9pm last night.
Speaking to RTÉ's Sean O'Rourke, Fr O'Fearraigh said he paused at the top of the hill and looked into the valley as he travelled to the area, aware by the scene below that tragedy had struck.
"It just makes no sense whatsoever, it is a terrible tragedy," he said.
"It was made clear when I arrived that it was a terrible tragedy and horror. We stood altogether and we had a few prayers when the family members arrived.
"We stood still and we spoke and we embraced. Sometimes in tragedies like this, words can fall silent and I think that your presence and the presence of one another is what's important.
"These communities have been plunged into the depths of grief and mourning in this most tragic of events."
Fr O'Fearraigh said nothing can prepare you as a priest for tragedy, but said he is comforted by the fact that there is a strong community in the north-west and people will help each other. He also paid tribute to the emergency services at the scene.
"Their dedication is next to none," he added.
"It's important we have that and it's important to acknowledge it.
"They don't seek praise, but it's important to say thank you."
Parish priest for Gortahork Fr Sean O'Gallchóir said it is a tragedy that spans three parishes in north-west Donegal.
Speaking earlier this morning on RTE Radio One's Morning Ireland, Fr O'Gallchóir said there will be a "void" for the parents for the rest of their lives.
"People are just saddened and stunned, and in disbelief and totally numb," Fr O'Gallchóir said.
"On behalf of everyone, we extend our sympathies to the parents, to the families and friends of the four young men.
"It is felt right across the communities as they come from three different parishes, two of the young men are here in Gortahork, one in neighbouring Falcarragh and one in the parish of Gweedore, very well-known young men and very well-known families."
Fr O'Gallchóir said he spoke to two of the families last night after the accident.
"The two boys were in the same class in primary school, the same class in secondary school, they grew up together. They were friends all their lives," he continued.
"I was talking to the parents last night and it just beyond belief. They are totally devastated and in shock and in great grief.
"The community will rally around, people will do their best, but this will be a void for the rest of the parents' lives."
The local priest said people in the area are "bewildered" by the tragedy.
"It's unbelievable for young people to see, these boys they grew up, they went out with."
Local Sinn Féin TD Pearse Doherty said there was a "cloud of sadness over the area", adding that his thoughts and prayers were with the dead men's families.
He paid tribute to the four men, saying they had their full lives ahead of them.
"As the news filtered through, a cloud of sadness descended on the entire area. When you hear of a tragedy like a car crash, you fear the worst. This was beyond the worst.
"These were four friends who had all their lives in front of them, and they had their lives snatched from them."
Fianna Fáil TD for Donegal Pat the Cope Gallagher expressed his shock and sadness.
“My thoughts and prayers are with the families and friends of these men. I know the community will rally around the families over the tough days and weeks ahead.
“I would like to pay tribute to the Gardaí and the emergency services and first responders, who arrived swiftly on the scene and tended to the victims."
The four deaths bring to 10 the number of people who have lost their lives on Irish roads over the last week.
Last night, a man in his eighties lost his life in a single vehicle collision near Coolcullen in Co Kilkenny.
On Friday, Joseph and Louise Waller, who were both in their 70s, were killed in a single car crash near the Monaghan and Armagh border at Killyneill Cross.
Their car left the road and ended up in a bog. It is believed their car had become submerged in water.
On Thursday, a pedestrian in his 40s died after he was struck by a 4x4 vehicle on the Dublin Road, Monasterevin, Co Kildare.
Earlier that day, Dublin woman Jackie Griffin was killed in a collision on the M50.
And after 9am on the same day, a passenger in her 80s died after the car she was travelling in was involved in a collision in Loughrea, Co Galway.
Last Sunday night, a 60-year-old man was involved in a collision with a truck in Dungarvan, Co Waterford.