Juress Kika, 19, Jade Braithwaite, 18, and Michael Alleyne, 20, were convicted by a jury at the Old Bailey.
Ben and his friends had been to a bar to celebrate the end of their GCSE exams when a row broke out in Islington, north London, on June 29 last year.
Although the confrontation had nothing to do with him, he was chased along the street with other youngsters - and stabbed to death when he stopped running.
Ben was stabbed 11 times in five seconds by the three youths in revenge for the "disrespect" shown to Braithwaite earlier.
After the verdicts, it emerged Kika had been on the run from police for 10 days following a robbery in which a man was knifed on June 19.
Three other youths were arrested but despite extensive searches and inquiries, Kika was not found until he was arrested for Ben's murder at a flat in Chadwell Heath, east London, on June 30.
The 21-year-old victim, who appeared to have been involved in a row about drugs, refused to press charges.
Alleyne was being supervised by the local youth offending team as part of an 18-month detention and training order for drug dealing.
He had been released three months earlier after serving half the sentence in a detention centre.
Miss Kinsella appeared tense and sat with her fingers crossed as the jury of four women and seven men came into the courtroom.
The defendants were led in in handcuffs and stood between prison officers in the dock.
There were shouts of 'Yes' from members of the Kinsella family when the verdicts were announced.
Some people in the public gallery applauded.
Ben's mother Deborah started sobbing after the first guilty verdict was delivered.
The killers were remanded in custody for sentencing tomorrow.
Ben had been part of a large, happy family consisting of his mother Deborah, 46, father George, 48, Brooke, 25, and her two sisters.
Ben did well at school, wanted to be a graphic designer and had many friends.
Some 400 people joined the family to march against knife crime following his death.
The defendants had admitted punching Ben but each denied he was the knifeman.
Detective Chief Inspector John Macdonald said the first row in the pub had "materialised out of nothing".
But it had led to Braithwaite seeking out Alleyne and Kika - resulting in them stabbing someone who had nothing to do with it to save face.
He said: "I think it is done out of pure ignorance. People seem to resort to the most serious violence, particularly young people.
"They are people who are ignorant and socially inept. Young people become desperate about being disrespected.
"Braithwaite probably thought he had been disrespected by one of the younger kids and wanted to take retribution, to take revenge."
After the verdicts a tearful Mrs Kinsella read a victim impact statement to the court in which she said her son's killers would never know the pain they had caused to her family.
She said: "The people who murdered him knew nothing about our Ben, not a hair on his head, a bone in his body, not anything about our wonderful son.
"They had never met him before or spoken to him, they just cruelly took his life away with knives for no apparent reason.
"We had brought Ben up to always walk away from trouble. This sadly cost him his life.
"He walked away to get safely home and they took advantage of that - he was one boy on his own.
"It seems unfair. Their intent was to stab someone that night."
She added: "We as his family have been left devastated and in total despair. Our whole world has been totally turned upside down.
"Ben went for a good night out and never came home again."
Ironically, Ben never lived to find out his "wonderful" exam results.
Mrs Kinsella said: "Ben had only just finished school - a straight A student, he had a job and had got his place in college.
"Ben loved life, he loved living, and he had so much to live for. He knew where he was going and where he wanted to be.
"Ben loved nothing more than to make people laugh, he was a fun-loving, happy-go-lucky boy with a heart of gold and would do anything for anyone."
Brooke Kinsella and her family had wiped away tears as CCTV images were shown to the jury in which Ben could be seen staggering around after being stabbed.
Nicholas Hilliard QC, prosecuting, told the court: "No one suggests Ben Kinsella was anything other than totally blameless."
Mr Hilliard said Ben and some of his friends had left Shillibeers bar in North Road, Islington, shortly before 2am.
A crowd had gathered outside after a row between Braithwaite and his friends and a group known to Ben, spilled outside.
Braithwaite had been heard to say: "Tell your boy if he wants trouble, I've got my tool on me and it will open you up."
Ben and his schoolfriends decided to leave as the group dispersed.
Braithwaite ran off to look for back-up and returned with Alleyne and Kika, chasing the crowd of boys and girls.
"There had been all that posturing by Mr Braithwaite. It seems he had been chased away but that his reputation was at stake," Mr Hilliard said.
He went on: "They managed to catch up with the deceased, knocked him from his feet at the rear of a parked van and, as he lay on the ground, launched a lethal attack upon."
Young friends of Ben gave evidence to the court. Some of them broke down as they recalled the events of the night.
Claudia, who was 16 at the time and cannot be named in full, said: "The boys started to run. Ben crossed the road and stopped running.
"Ben said 'What are you coming over to me for? I haven't done anything'."
She said 6ft 6in Braithwaite "kicked Ben in the belly and he fell to the floor".
"I thought they were punching him but I couldn't see," she said.
Alleyne and Kika were arrested at the home of a teenager called Kellie who told the court she overheard them confessing to the murder.
Alleyne had told her he had received a call from a friend for back-up at a party where there was trouble.
Members of the jury fought back tears as Mrs Kinsella read her statement out and her daughter Brooke sobbed.
The court was also given details of the killers' previous convictions.
Braithwaite had been given a community order for an attempted robbery.
Alleyne was a convicted heroin and cocaine dealer who also had convictions for robbery and possession of cannabis.
Kika had convictions for cannabis possession, robbery, affray and for restricting or obstructing a constable.
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