The boy, identified as Arion Lilly, was hit Thursday near 11th and Rutledge Street on the city's West Side.
No one was in custody Monday afternoon. Police are searching for a red Chevy Impala, which is believed to be involved in the shooting.
The Gary Middle School student was shot once in the back as people in two vehicles were shooting at each other.
Gary Police Cmdr. Jack Hamady said they were initially called to the scene to investigate shots fired. It wasn't until some time later when officers searched the area and found Lilly's body lying in this vacant lot.
"He was laying there by himself," Hamady said.
His mother Cheryl Freeman saw the police activity nearby, but didn't pay it much attention.
"I was never thinking that was my child," said Freeman. "So when the hours went past and he hadn't made it home. It still hadn't clicked with me that was my son out there."
Gary police released a photo of the red Chevy Impala believed to be involved.
"We believe between 2006 and 2013. It has a spoiler, tinted windows, a dent on the rear passenger bumper and a dent on the passenger side. Distinct. We believe it has Indiana plates on it," Hamady said.
As the search for Lilly's killer continues, his stepfather Ernst Dextra paid tribute Monday to the young man he was growing up to be.
"I stressed on him to be respectful to his elders and just being a role model himself. And he really took that to heart. Everybody around him loved him," Dextra said.
To the shooters, Freeman said: "You took away an amazing kid. He had dreams. He wasn't a gangbanger. He wasn't about that life at all. He was about school life. Graduating. Going to college."
Arion's family said he loved basketball and making people laugh.
"As a mother, this tragedy is hard to imagine," stated Mayor Karen Freeman-Wilson. "As the leader of this city, we are laser focused on bringing Arion Lilly's killer to justice. I stand with his mother, Cheryl Freeman and we are wrapping our arms around his family."
Anyone with information about the shooting is asked to call Gary Police Det. Cpl. James Bond at 219-881-1209 or 755-3852.