Rhyhiem Ainsworth Barton was found with a fatal gunshot wound in Southwark at about 6pm on Saturday.
Armed police attended the scene and he was given first aid by paramedics but died shortly before 7pm.
Rhyhiem’s mother, Pretana Morgan, paid tribute to her son – an aspiring architect and rapper – and criticised police for “putting us in danger”.
She told reporters: “I couldn’t have asked for a better son. My son was a very handsome boy. He’s got so much potential.”
Ms Morgan said Rhyhiem was “trying to make a difference” by learning to work with children.
“This is not life. My son’s a good boy,” she said.
“I need to hold him. My handsome boy.
“We’re not being protected because of the police. The police are the ones putting us in danger.”
Ms Morgan, who also has a six-year-old daughter, insisted her son was not involved in gangs and said it was not the first time he had been targeted.
She claimed the culprits were from a gang from outside the area and made an emotional appeal for young people to end the recent spate of violence in London.
“I want them to stop this,” she said. “I want these children to stop this.
“Teenagers need to stop. Enjoy your life. Enjoy your youth.”
Rhyhiem’s godmother Lacey Main said he had been shot at by someone in a car.
“Any loss of life is a loss,” she said.
“It doesn’t matter where they come from. It doesn’t matter what religion, what culture, what skin colour… a life is a life. A young life is a young life.”
London Mayor Sadiq Khan said he had been in contact with the Metropolitan Police Commissioner about the “appalling crime” and the force was “doing everything they can to bring those responsible to justice”.
No arrests have been made and detectives from the Homicide and Major Crime Command are investigating.
The fatal shooting is the latest violent crime to hit London amid concerns about the capital’s rising murder rate.
Sky News has identified 60 people who are suspected to have been deliberately killed in London since the start of the year.
On Tuesday, a man believed to be in his 30s was killed after a shooting outside Queensbury Tube station in northwest London.
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The latest killing comes after Donald Trump compared a London hospital to a “war zone” because of the spate of fatal stabbings in the capital this year.
The US president’s remarks at a pro-gun rally in Texas were later branded “ridiculous” by a surgeon working in the capital.