A 13-year-old boy is the fourth person arrested in connection with the murder of Ozell Pemberton.
The teenager handed himself in to a police station on Monday and was arrested on suspicion of murder.
Ozell, 16, was found with chest injuries in Lower Parade in Sutton Coldfield on Thursday afternoon.
A 17-year-old, from Lozells, appeared at Birmingham Crown Court charged with the murder and was remanded in custody.
A 21-year-old, from Erdington has been released on police bail while another 17-year-old, from Kingstanding, remains in custody.
A post-mortem examination found Ozell died from a stab wound to the chest, police said.
His parents said their "special boy" was "one of a kind".
A fundraising page, set up by Ozell's family and friends to cover the cost of his funeral, has received more than £1,500 in donations.
Amber Silk, 17, of Castle Vale, a friend of the victim, said: "Ozell was so lively, so full of energy, and had a really kind heart."