The incident began at about 10:15 p.m. when police were called to an apartment complex in the 21600 block of 29th Avenue where a large noisy party was under way in the parking lot, said Sgt. Doug Jenkins of the Des Moines police.
Officers cleared the area and shuffled everyone away from the scene.
At about 10:55 p.m. police were called back to the same address, where they found about 100 people - mostly teenagers - still loitering in the area, Jenkins said.
Officers then heard several gunshots down the street and found a 17-year-old boy who had been shot twice in the arm. He was taken to Harborview Medical Center for treatment of non-life-threatening injuries.
Meanwhile, more gunfire broke out nearby. Police responded and found a car with its window blasted out. Another round went through the wall of a neighboring apartment but no one was struck.
Investigators still haven't been able to determine what led to the gunshots, and no suspect description is available at this time, Jenkins said.