The killing is the fifth homicide in six days in the capital.
The boy is the 13th teenager to die in a knife attack this year, just two short of the 15 in 2020 and on course to overtake the figure of 26 in 2019.
Police were called on Friday evening to Church Road, Harold Wood, east London, following reports of a fight involving a number of youths.
The victim was found suffering from a stab injury and died at the scene.
Witnesses said he had been set upon by machete-wielding thugs in balaclavas and chased out of the park.
Ten minutes later, two boys aged 15 and 17, were found with stab wounds nearby. They have been arrested on suspicion of murder and were continuing to receive treatment in hospital today. Another 16-year-old boy was arrested on suspicion of affray.