The teen killed has been identified as Khalief Webster, according to family.
"When I see the news and clips on social media of young men being gunned down, I sit there and I mourn for their parents," said Webster's mother, Talaya Shaw. "Now, I'm mourning my son."
It happened near Long Lane and Pine Street, not far from Webster's home, just before 3 p.m. on Sunday.
Upper Darby Police released video and pictures of the suspect.
They say the victim and another boy were involved in an argument when one of them pulled a weapon and shot the teen in the back.
"As parents, we try so hard," Shaw added.
"It's like a nightmare," said Webster's stepdad, Jeffrey Stamps.
Webster's family told Action News that he loved playing sports in the neighborhood with his siblings and friends. They also said he loved to work, holding several jobs, and couldn't wait to join the workforce full time.
"He loved to work," Stamps said, recalling, "I was telling about opportunities in trade unions and construction. He was like, so excited. He was looking forward to graduating and just moving forward and just being -- becoming a young man."
The police department says it is working with the Upper Darby School District to provide resources and support for the victim's family, students and staff.
Anyone with information or recognizes the suspect is asked to call Upper Darby Police at 610-734-7693.