Story highlights Zarriel Trotter, 13, has advocated against gun violence in Chicago

He was struck by the lower back by a stray bullet on Friday

In PSA, Trotter says: "People keep on getting shot, people keep on getting killed"

(CNN) Zarriel Trotter joined other boys in a sobering public-service announcement last year to voice fear, hopelessness and sadness about gun violence on the streets of Chicago.

"I don't want to live around my community where I've got to keep on hearing and hearing people keep on getting shot, people keep on getting killed," Zarriel said in the video, which closes with the message: "The loss of a black boy is a loss for America."

On Friday, the 13-year-old was shot in the lower back by a stray bullet fired during a heated argument on a street several blocks from his home, according to the principal of his school and the co-CEO of the firm that produced the video.

"It's really heartbreaking to hear one of your students has been hurt in this way," said Elizabeth Jamison-Dunn, principal at Catalyst Circle Rock Charter School, where Zarriel is a seventh-grader.

It was the kind of shooting Zarriel said in the video he was growing tired of hearing about in his community.

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