Holly was last seen in Young Street, Frankston around 5pm on 30 November.
Officers have concerns for the welfare of the 12-year-old due to her age.
Holly is known to frequent the Frankston CBD.
She is described as Caucasian, 160cm tall, thin with blonde shoulder length hair and blue eyes.
Investigators have released a photo of Holly in the hope that someone may have information on her current whereabouts.
Anyone who sees her is urged to contact Frankston Police Station on 9784 5555.
