The two were shot Tuesday evening near 59th Street and Francisco.
Chicago police say a gunman fired on the victims before running away.
The shooting killed Darryl Manns, 22, who lived nearby. Authorities said he was shot in the head and leg and found dead at the scene.
A 15-year-old boy was shot in the back and buttocks and taken in critical condition to Mount Sinai Hospital initially, but he later died there, police said. His identity was not being made public immediately.
Police said Wednesday they did not have a suspect .A possible shooter was seen fleeing the scene wearing a grey tank top and black jeans, Chicago Police News Affairs Officer Veejay Zala said.
Authorities also did not know the motive for the shooting.
(The Sun-Times Media Wire contributed to this report.)