Chloe Egan (15) was last seen leaving an address in Woodburn Crescent at about 8am on Wednesday, May 22.
Kimberley McGrory, who is also 15, is last known to have left a property in Burnside Drive at about 12am on Thursday, May 23.
Police are now appealing to members of the public for information.
Chloe is described as white, 5ft5, of medium build and has shoulder-length brown hair.
Forth Valley officers say she is possibly wearing a black jeans and a hoodie and has links in the Bonnybridge, Denny and Falkirk areas.
Kimberley is described as white, 5ft7, of slim build and long brown hair. She is possibly wearing grey tracksuit bottoms, a blue hoodie and white trainers and has links in Bonnybridge and Denny.
Anyone who may have seen Chloe since this time, or who has any information on her whereabouts, is urged to contact Police Scotland via 101, quoting incident number 4353 of May 22.
Those who might have information regarding Kimberley’s whereabouts are asked to contact the same number and quote incident number 2373 of May 22.