Munshi was said to have spent hours on jihadist websites
Three men have been found guilty of possessing or making documents promoting terrorism.
The defendants included Hammaad Munshi, 18, from Dewsbury, West Yorkshire -thought to be the youngest person to be convicted under the Terrorism Act.
He was 16 when police found a guide to making napalm on his computer, Blackfriars Crown Court heard.
Aabid Khan said to be a "key player" in radicalisation via the internet and Sultan Muhammad were also convicted.
Khan, 23, from Bradford, West Yorkshire, was found guilty of possessing articles for a purpose connected with terrorism but cleared of a similar charge.
Muhammad, 23, from Manningham, West Yorkshire - Khan's cousin - was convicted of three similar charges and one of making a record of information likely to be useful in terrorism.
Munshi was found guilty of making a record of information but cleared of a possession offence.
A fourth defendant, Ahmed Sulieman, 30, from south London, was cleared of three possession charges after telling the jury the files found belonged to somebody else.
Khan and Muhammad will be sentenced on Tuesday.
Munshi, who had been on bail throughout the trial, was remanded in custody until 19 September when he will be sentenced at the Old Bailey after the preparation of a pre-sentence report.
Khan was arrested at Manchester Airport on 6 June 2006 as he arrived back from a trip to Pakistan.
Prosecutor Simon Denison said DVDs and computer files were seized and showed Khan had a "deep commitment to and involvement in violent jihad".
This included "inciting others to take part in it and arranging for himself and others to attend military training in Pakistan in preparation for going to fight and, inevitably, to kill".
Further raids followed in West Yorkshire, leading to the detention of Khan's co-accused.
Mr Denison said the men had been "motivated by their common cause" and had amassed computers, CDs and books that "were the necessary tools of their trade, possessed to be used in furtherance of that violent cause".
Diaries were among the documents found by police
Munshi was said to be just 15 when recruited by Khan.
The court heard the teenager spent hours surfing jihadist internet sites, speaking to Khan, and distributing material to others.
He did not not give evidence in his defence, but his barrister suggested the case showed "curiosity" as opposed to any kind of malicious intent.
After the convictions, Det Chf Supt John Parkinson, head of Leeds Counter Terrorism Unit, said: "Let there be no doubt, these are dangerous individuals.
"These men were not simply in possession of material which expressed extremist views. They were also in possession of material that was operationally useful to anyone wishing to carry out an act of violence or terrorism."
He added: "While these men may not have been actively planning acts of terrorism themselves, they sought to incite others for terrorist purposes, promoting al-Qaeda ideology and training programmes."