Scott Kouebitra, 22, was attacked in Croydon, south London. Four others also suffered knife wounds.
Police said they were searching for a group of about seven males who fled the scene in two cars and were wearing masks, scarves and balaclavas.
The 16-year-old boy was also arrested on suspicion of robbery and is in custody.
Scotland Yard said the group of males arrived at Gloucester Road in two vehicles and entered St George's Field Park carrying weapons.
Det Ch Insp Sam Price said there were "a large number of people in and around the park" at the time and appealed for witnesses to contact the force.
A post mortem examination found Mr Kouebitra died of multiple stab wounds.
The four other men suffered non-life threatening injuries.
A teenager has been arrested on suspicion of murder after a man was stabbed to death on Halloween.