Pretana Morgan described the streets of the capital as "paved with blood" after she found her son dying from gun wounds near their home in Kennington last night.
Officers were called to reports of gunshots on Cooks Road, just after 6pm and found Pretana's son, Rhyhiem Ainsworth Barton, dying on nearby Warham Street.
Medics rushed to save his life but the teenager was declared dead at the scene.
"This is not life. My son's a good boy," she added.
She told how the rapper and aspiring architect had returned to London just a few weeks before after she sent him abroad to live with relatives in Jamaica after he was knifed in the capital.
Ms Morgan, who wept as she talked about her son, said: "I need to hold him. My handsome boy."
She added: "We cannot be doing this all the time, teenagers you need to stop please.”