The seventeen-year-olds have been named as Hassan Munshi and Talha Asmal, who are thought to have fled to the war-torn country after travelling to Turkey on March 31.
The boys from Dewsbury were last seen by their families on the day they are believed to have flown from Manchester to Dalaman, West Yorkshire Police said.
A statement released on behalf of the two families said: “Both families are devastated by the events of the last few days and in particular, we are extremely concerned about the safety and well-being of our loved ones.
“Our number one priority is to get Hassan and Talha back home with their families and we implore anyone who may have any information whatsoever to get in contact with the police.
“Naturally, we are in a state of profound shock and are trying to come to terms with the predicament we find ourselves in and we hope and pray that no other family finds itself in our situation.
“These were just two ordinary Yorkshire lads who enjoyed the things that all young people enjoy at their age - both Hassan and Talha had a promising future as an apprentice and an A-level student respectively, and we are praying they will be back with us soon and are able to realise that future.
“We would implore all parents to be extra vigilant, although as we found, it’s near impossible to know your children have been groomed and brainwashed.
“Syria is a frightening war-torn place and we need to urgently educate our young children about the dangers posed by those who prey on impressionable teenagers.”
According to reports Talha Asmal and Hassan Munshi have been missing for several days and their families contacted the authorities after becoming concerned.
Hassan Munshi, according to The Times, is a relative of Hammaad Munshi, who was 15 and Britain’s youngest convicted extremist when he was arrested by counter terrorism police in 2006.
Searches for the pair, who are said to be “best of friends”, are reported to have focused on the Turkish side of the Syrian border, but they are now believed to be in Syrian territory.
Hammaad Munshi, of Greenwood Street, Savile Town, was just 15 when he discussed jihad online. He should have been revising for his GCSEs at Westborough High School in Dewsbury when he began downloading notes on manufacturing deadly napalm instead.
He hid notes under his bed expressing his burning desire to go abroad to kill in the name of Islam.
Munshi was convicted in 2008 when he was 18 and sentenced to two years in a young offender institution.
Today the North East Counter Terrorism Unit confirmed that two 17-year-old boys had left Dewsbury and were believed to have travelled to Syria.
Assistant Chief Constable Mark Milsom of West Yorkshire Police, said: “We are extremely concerned for the safety of these two boys and would urge anyone with information to come forward and speak to us.
“Our priority is for their safe return; their families are gravely worried about them and want them home.”
The boys were last seen by their families early on Tuesday March 31 and are believed to have boarded a Thomas Cook flight at Manchester Airport later that day to Dalaman in Turkey.
Mr Milsom said: “Syria is an extremely dangerous place and the public will be aware of the dangers these boys may face. The choice of returning home from Syria is often taken away from those that come under the control of Islamic State, leaving their families in the UK devastated and with very few options to secure their safe return.
“Anyone who is concerned that a friend, family or relative may be contemplating travelling to Syria can discuss with the local police or local authorities safeguarding units either by contacting 101 or attending their local neighbourhood Policing teams.”
He added: “This is not about criminalising people. It is about preventing tragedies by offering support to communities, families, young and vulnerable people.”
Shahid Malik, the former Dewsbury MP who has been in contact with the families of the missing teens, said they were “completely distraught”.
He told ITV Calendar today: “Their first priority is to get their young children back. They are young children, they are 17-year-old boys, best of friends, but the families are desperate to get some news about them to know they are well and to get them back home as quickly as possible.
“At this moment in time they haven’t got a clue what is going on. They are completely in shock because there was no inkling that anything like this could possibly happen.”
Kirklees Council chief executive Adrian Lythgo said: “We are deeply concerned for these young people and will continue to work in close partnership with the Counter Terrorism Unit, West Yorkshire Police, our communities and schools to prevent and eradicate any threats and concerns.
“We need to talk openly about these risks that are posed to our young people, and to work together to protect them. Communities and families can contact police about anyone they feel may be vulnerable. This includes anyone who is showing signs of becoming radicalised, who may have returned to the UK from Syria or may be planning to go to Syria or another conflict zone.”
The Metropolitan Police believe around 600 Britons have travelled to Syria and Iraq since the conflict began, while around half are believed to have returned to the UK.
Nine Britons - including the son of a Labour councillor - were arrested in Turkey last week on suspicion of trying to cross the border into the neighbouring war-torn country.
Waheed Ahmed was one of five adults and four children being held by Turkish authorities after they were stopped in Hatay province last Wednesday.
Meanwhile, teenage girls Shamima Begum, Amira Abase and Kadiza Sultana are believed to be inside Syria after flying to Turkey in February.
It is understood the Bethnal Green Academy pupils from east London were following another 15-year-old girl who travelled to Syria in December.