Butler was last seen at Tesco Superstore, McConnell Drive, Wolverton on Saturday, July 31, at about 12pm, wearing a light grey coloured top, grey hoodie and faded jeans.
Atlanta is described as approximately 5ft 2ins tall, with dark brown very long hair and of a slim build.
Officers are getting worried about her safety.
Inspector Steve Raffield, based at Milton Keynes police station, said: “We are becoming increasingly concerned for the welfare of Atlanta and are appealing for the help of the public in finding her.
“I would urge anyone who may have seen Atlanta, or anyone who thinks they know where she is to please get in touch by calling 101 quoting reference 43210342020.”