The robbery occurred in the Hollenbeck area around 1 p.m. last Monday.
Authorities say the girl was walking near Cesar Chavez Avenue and Fickett Street when the suspect walked up to the victim and pulled the gold chain off her neck.
The suspect, last seen running from the location, is described as a black male, between 20-25 years old, approximately 6 feet 3 inches tall, and weighing 180 pounds.
Nearby surveillance camera footage shows the suspect buying a soda just minutes before the robbery.
Detectives believe the suspect may be responsible for similar crimes in the area.
Anyone with any information regarding the crime is urged to contact the LAPD at (877) LAPD-24-7.