Tony Eastlake, 55, was killed after being attacked near his flower stall at around 5.30pm on Saturday.
He had worked as a flower seller on Essex Road for 41 years and was much-loved member of the local community.
Witnesses said he had tried to stop a mugging.
Mr Eastlake was treated by paramedics but was pronounced dead at 5.58pm.
In a statement released through the Metropolitan Police, his family appealed for people to come forward with information about the father-of-one’s “violent and unnecessary” death.
They said: “Our hearts are broken forever at the loss of such a very special man.
“A man who was loved by everybody in the Islington community, who is remembered as kind and caring and always laughing, but most importantly a father who leaves behind a devastated family, Lisa, Pauline, and his only daughter and best friend Paige, who he adored.”
Mr Eastlake’s family said he had worked on the flower stall since he was 14-years-old and was always there “rain or shine”.
They said he was a “smiling and friendly face” to many in the community and that they had received hundreds of messages of support following his death.
“We ask you now please for your support in helping us to find the person or people who did this to our family - who took away a life so violently and unnecessarily,” they said.
“If you have any information at all we beg you to please come forward so we can get justice for Tony and his family.”
Officers from the Met's specialist crime command have launched a murder investigation.
Detective Chief Inspector Vicky Tunstall, leading the investigation, said: “We have a dedicated team of officers working around the clock to find the person or people responsible and I would like to hear from anybody who could help out investigation.
“I am particularly keen to hear from people who were in Halliford Road or Ecclesbourne Road between 17:20hrs and 17:25hrs.
“Did you see Tony? Or did you witness an altercation, or see anyone running away?”
She said she was also appealing to people who lived in the area who may have private CCTV to come forward.
“I would very much like to hear from delivery drivers and owners of cars with dash cams who were travelling through the area at the time of the incident,” she added.
“You may have captured significant footage that we need to recover as soon as possible.”
Detectives are considering several possible motives and are “keeping an open mind as to the circumstances behind the attack”, a spokesperson said.
A post-mortem examination is due to take place soon and no arrests have been made to date.
Many people living locally to Mr Eastlake’s stall paid tribute to him on the Islington Community Group on Facebook.
Francis OBrien said: “Such such sad news, my thoughts are with Tony’s family and loved ones.
“Tony had a kind heart, served our community for a number of years and always put a smile on the faces of people across Islington.
“He was not just a local businessman, but a friend to many.”
Andres Paniagua Toro said: “What a very sad day, the community has lost a great human being who helped many people daily with his beautiful smile and willingness to listen to their woes.”
He added: “Tony would always make me smile every morning on my way to work.”
Elsa Smurthwate posted: “How very very tragic. RIP fella, a true islingtonian and a man who also had time to smile and say hello. Him and his stall have literally been one of the few things that stood the test of time x”
She added: “I hope the council would consider his stall to be left as a shrine in his memory.”
Garry Clowes said: “God rest Tony, always enjoyed pulling up for a chat and a cuppa. London’s slowly being crushed.”
A vigil has now been planned close to Mr Eastlake’s Essex Road stall at 6pm on Monday evening by members of the community, while a GoFundMe page has been set up to cover the cost of his funeral.
Anyone with information is asked to call police on 101 quoting reference CAD 5562/29May. To remain anonymous, contact Crimestoppers on 0800 555 111.