There needs to be a "vast improvement" in communication between police, schools and parents to prevent young Britons from fleeing to Syria to join Islamic State, a group of MPs has said.
In a report on so-called foreign fighters, the Home Affairs Select Committee described the UK as being "at the edge of a cliff" in the battle to block radicalisation.
It called for a strong "counter-narrative" to win the "hearts and minds" of those at risk.
While it recommended greater involvement by social networking companies, it conceded that "policing social media sites is impossible," adding that young people must be given the skills needed to resist radicalisation online.
The report comes after three teenage schoolgirls from London successfully fled to Syria to join Islamic State.
In the report Mr Vaz said that there was no "immediate action" taken in the case of Amira Abase, Shamima Begum and Kadiza Sultana - which should be seen "in contrast" with the speed with which police worked to return three teenage boys from Brent who were stopped in Turkey as they attempted but failed to do the same.
The Metropolitan Police defended the speed with which the force responded to the disappearance of the three schoolgirls following what it called the committee's "misleading" criticism.
A spokesman said the girls were reported missing on the Tuesday, and the following day the police contacted the liaison officer in the Turkish embassy in London and the British Consulate in Istanbul. An officer was on the ground in Turkey on Friday, he said.
The force recently apologised for failing to communicate more directly with the missing girls' families, but insisted there was nothing more it could have done to stop them from leaving.
'Foreign fighters' report recommendations:
Setting up an "advice service" targeted at parents
Social media giants such as Twitter and Facebook should suspend the accounts of users who seek to promote violent extremism
Home Office should work with airlines serving so-called "destinations of concern" such as Syria, Somalia, Iraq and Nigeria to develop stricter controls for passengers travelling there
Police to work faster to alert overseas partners and airlines