Leftridge reportedly was last seen at approximately 3 a.m. Sunday near 13th and Kedvale. She had been visiting her father for the weekend.
The teen girl attends 0T Bright Elementary School at 107th Street and Calhoun.
Her parents say she has never run away before and wonder if she could have met someone on the Internet.
Anyone with information on Leftridge's whereabouts is asked to contact Chicago police.