The men, led by ringleader Reece Chisholm, 37, say they are sickened by the state of Hall Green in Birmingham after the killing of 12-year-old Leo Ross in January.
Leo was found by a member of the public with a stab wound to the stomach on the banks of the River Cole, close to Scrivers Lane, on January 21. He died in hospital at 7.30pm that evening.
West Midlands Police arrested the youth, who cannot be named because of his age, on Tuesday, around four hours after Leo, aged 12, suffered fatal injuries on a riverside path.
A teenager being quizzed by police in connection with the murder of a 'kind' 12-year-old schoolboy has been further arrested over assaults on three pensioners aged in their 70s and 80s.