The incident happened just after 3 p.m. Thursday near Studebaker Road and Keynote Street.
According to the Long Beach Police Department, a female victim was in the area when two men in a vehicle approached her.
"Upon exiting the vehicle, one of the suspects engaged the victim in a physical altercation, which resulted in the suspect robbing the victim," said police in a statement.
Witnesses say the victim is a middle school student.
Both suspects fled the scene before officers arrived. No injuries were reported and the suspect reportedly got away with the victim's necklace.
The incident remains under investigation. Anyone with information is urged to contact police.