The two fans were on their way to New Zealand to watch their team in a pre-season tour.
The pair have been named as Liam Sweeney and John Alder, both understood to be well known figures at St James' Park.
A message on Newcastle United supporters website, The Mag, reads: "Our hearts go out to those families and those friends who were closest to them.
"It is a tragedy though for all Newcastle fans and we hope everybody, whether they knew them or not, gives a minute to think about their loss, as well as all of those other people who tragically lost their lives on that flight."
Mr Alder, thought to be in his 60s, was known to fans as 'The Undertaker' because he always wore a suit to the match.
A former BT worker from Gateshead, Mr Alder had only missed one Newcastle match since 1973 and travelled to every away match.
He was on his way to New Zealand with Mr Sweeney, 28, thought to be from Newcastle.
Mr Alder's neighbour in Gateshead, Margaret Bambra, 66, said: ''I have known him for about 40 years. We all knew him as 'the Undertaker' because he always wore a black suit and white shirt to every match.
''He was a lovely guy, never bothering anyone. He went to every game, he never missed a match. He was Newcastle-mad.
''I really cannot believe it - it's totally devastating. He did not deserve this.''
Meanwhile, David Cameron is to chair a meeting of the Government's emergency Cobra committee after nine Britons were among those killed when the passenger plane was downed over Ukraine.
Pro-Russian rebels are being blamed for shooting down the the Malaysia Airlines Boeing 777-200, which was carrying 298 people from Amsterdam to Kuala Lumpur.
Kiev has branded the event an "act of terrorism" and demanded a UN investigation, while Russian president Vladimir Putin has insisted it would not have happened if the Ukrainian government had agreed to a ceasefire.
Up to 100 of those killed on flight MH17 were delegates on their way to an international conference on Aids in Melbourne, Australia. They included world-renowned researcher Joep Lange and 49-year-old Glenn Thomas, a British media relations co-ordinator for the World Health Organisation and former BBC journalist who lived in Blackpool.
According to the airline, there were 154 Dutch passengers, 45 Malaysians, including 15 crew, 27 Australians, 12 Indonesians, four Germans, four Belgians, three Filipinos and one Canadian on board.
Three infants are among the dead and the nationalities of 41 passengers have yet to be verified. New Zealand authorities have also reportedly confirmed that one of its nationals died in the crash.
The plane was flying on a usual route that had earlier been declared safe by the International Civil Aviation Organisation, Malaysia Airlines said, while the International Air Transportation Association said the airspace it had been crossing was not subject to any restrictions.
All European flights operated by the airline will be taking alternative routes with immediate effect.
One British family appears to have had a miraculous escape after changing flights at the last minute.
Barry Sim, thought to be from Methlick in Aberdeenshire, told The Times he had tried to board the flight with his wife Izzy and their baby but could only get one seat. After hearing of the crash, he said: "You get this sick feeling in the pit of your stomach. We started getting butterflies. Your heartbeat starts going."
Foreign Secretary Philip Hammond has called for an international investigation to establish what happened to Flight MH17 when it crashed into territory held by pro-Russian separatists.
Speaking at the Foreign Office following emergency talks with ministers and officials, Mr Hammond said: "We're determined to get to the bottom of understanding what has happened here," he said.
"As yet, we do not have any definitive information about how this incident occurred and I don't want to speculate at this stage. We believe that there must be a UN-led international investigation of the facts."
He said Britain was prepared to make Air Accident Investigation Branch assets and specialists available to assist an investigation.
The Government's Cobra emergency committee will meet this morning, with the United Nations Security Council due to hold a session on Ukraine at 3pm UK time.
Ukraine's ambassador to Nato Ihor Dolhov told BBC Radio 4's Today programme: "Evidence and information we have as now confirms it was pro-Russians (who caused) this tragedy which took the lives of 298 people, including Brits - please accept our condolences.
"We intercepted and distributed scripts of phone calls from separatists to Moscow. This exchange by phone of information confirms that separatists are responsible and involved.
"But that's not the only evidence. The Ukrainian defence ministry clearly stated we didn't have any facility and any arms systems available at the region to act like that.
"We are ready to co-operate and we have requested additional information from all possible sources, including Nato headquarters."
Mr Dolhov said claims that separatist groups had seized Ukrainian army ground-to-air missile systems were "not confirmed", adding: "All Ukrainian systems of such kind are controlled by the Ukrainian defence ministry and armed forces."
Asked if this meant that if rebels were responsible for downing the plane, they must have done it with weapons supplied by Russia, Mr Dolhov replied: "Yes."
He said Ukrainian emergency services were at the scene of the crash, but it was difficult for the Kiev authorities to gain access to the site.