The photo shows only a man wearing a white T-shirt. No other details were immediately released.
Investigators said the party was held Monday night in a residential neighborhood in Bloomington.
Neighbors described it as a disruptive event and the sheriff's department estimated some 300 people were there.
The shots rang out around 1 a.m.
When deputies arrived, they found Robert "Robbie" Plyley, who was a sophomore at Alta Loma High School in Rancho Cucamonga, with gunshot wounds. He was taken to the hospital where he was pronounced dead.
The principal at Alta Loma High School said guidance counselors and therapists were being made available for students.
"Robert was a wonderful young man and his loss will be felt deeply by our entire school and District community," said Mathew Holton, superintendent of the Chaffey Joint Union High School District. "We are taking the necessary steps to support our students and staff, and will gather a team of counselors and therapists who will be available to provide additional support."
Investigators are asking anyone who might know the identity of the person of interest or his whereabouts to contact Det. David Carpenter at 909-890-4904 or We-Tip at 800-78CRIME.
You can also submit a tip on WeTip's website.