Both victims were innocent bystanders, police said.
Around 6:25 Thursday evening, police said at least six shots were fired as the two walked on Spruce Street between Van Cortlandt Park Avenue and Cliff Street in Yonkers.
The 13 year old victim was struck in the lower buttocks and the 31 year old victim was struck in the ankle.
Both were transported to a local area trauma center where they were listed in stable condition.
The suspect is described as possibly a black man in his 20's, 5'5" tall, with a thin build and wearing a purple hooded sweatshirt.
The suspect and another man were seen running south on Van Cortlandt Park Avenue.
The Detective Division is investigating this incident and anyone with information can contact them at 914-377-7724.