They were returning home after a holiday in Brazil with other friends who graduated with them from Trinity College Dublin two years ago.
They were named locally last night as Aisling Butler, of Roscrea, Co Tipperary, Jane Deasy of Dublin and Eithne Walls, originally from Belfast.
They were travelling together on the flight from Rio de Janeiro to Paris along with a fourth woman from Wales.
Aisling’s heartbroken father John said he couldn’t describe his family’s grief.
“We know Aisling is gone, we are sure of that,” he said. “It is just about trying to live now, I have to live for my wife and my only other daughter Lorna.”
When he heard about the missing plane he initially thought Aisling’s flight was due in the following day but decided to check the travel details in his deleted emails.
“When I opened it up a nightmare opened up as well,” he said.
Mr Butler said his daughter, who celebrated her 26th birthday just over two weeks ago, lived for her job as a young doctor but also enjoyed life to the full.
She was doing an internship in Tallaght Hospital, Dublin, and was due to move onto St James’s Hospital in the city next month.
“She never flunked an exam in her life, nailed everyone of them and took it all in her stride,” said Mr Butler, who owns an international transport company.
“She was a truly wonderful, exciting girl. I just can’t describe how we feel,” he said.
The young women had gone on a two week holiday to Brazil to visit other college friends who were travelling on to Australia.
Eileen Doherty, a friend of the Butler family, said Aisling’s mother Evelyn was seriously injured in a bad accident many years ago, although she has recovered.
“I always felt the Lord put a doctor in that family to look after Evelyn, and now she’s gone,” she said.
“She was such a lovely, cheerful, happy girl. Evelyn loved going to Dublin to see her, she was a laugh a minute.”
Irish President Mary McAleese said she was thinking about the families of the missing passengers.
“My thoughts and prayers, and the thoughts of everyone, this evening are with the Irish families and the families of everyone on board at this very difficult time,” she said.
Charles de Gaulle Airport in Paris, where the missing plane was destined for, is a popular hub for Irish travellers using the CityJet services from Dublin and Shannon to the French capital.
Foreign Affairs Minister Mícheál Martin said his officials have notified the families of the Irish passengers on board the plane which vanished this morning.
“We have contacted the families of those involved and are offering full consular assistance,” he said.
“It is clear from the passenger list that there are many people across Europe and in Brazil who face an anxious wait for news and our thoughts are with them during this difficult time.”
Irish embassies in both France and Brazil are keeping in close contact with the investigators.
All 228 people on board the airliner, including a baby and seven children, are feared dead.
The passenger list also includes 5 Britons, 61 French and 58 Brazilians among the 32 nationalities on board.
Air France said its Airbus A330 aircraft flying from Rio de Janeiro to Paris had run into stormy weather with strong turbulence around four hours into the flight.
About 15 minutes after the turbulence message, an automatic message was received from the plane – AF447 – indicating a failure in the electrical circuit.
Brazilian Air Force planes are searching for the missing aircraft.
Irish Taoiseach Brian Cowen said his government was deeply concerned and wanted to express its solidarity with families who are anxiously waiting for news of loved ones.
“Our primary concern is for the families during this difficult time,” he said.
“The government is offering support to the families as they wait news of their loved ones.”
Chief spokesman for Air France Francois Brousse said “it is possible” that the plane was hit by lightning.
Aviation experts said the risk the plane was brought down by lightning was slim.
“I cannot recall in recent history any examples of aircraft being brought down by lightning” said Bill Voss, president and CEO of Flight Safety Foundation, Alexandria, Virginia.
The prospect of finding any survivors from the disappeared jet is “very small,” French President Nicolas Sarkozy admitted last night.
Mr Sarkozy said “no hypothesis is excluded” in the search for causes of the disappearance of the flight.
The president was speaking at Paris’ Charles de Gaulle airport where he met some of families of those on board the plane. He said finding the plane “will be very difficult” because the search zone “is immense”.
Mr Sarkozy said France has asked for help from US satellite equipment to locate the plane.