Emma McDonald, 15, from Denniston Forge, Dumbarton, was last seen at her home by her dad at around 10am on Thursday, October 3, shortly before she left to visit her boyfriend and his family in Perth.
Emma's family reported her missing on Monday after she failed to return home.
Her family have been unable to contact her by telephone.
Police officers are attempting to find both Emma and her boyfriend, who has not been in contact with his family either.
It is believed the couple may be using a white Ford Ranger pick up truck.
Emma is described as white, around 5ft 4ins, slim with long black hair. She was last seen wearing red jeans and a pink top.
Local police from Dumbarton are working with colleagues in Tayside to try and trace both Emma and her boyfriend.
Police Inspector Gerry Boyd of Dumbarton Police Office said: "When Emma left her home on Thursday morning, she travelled to Perth to stay with her boyfriend and his family. She has not returned home and her family have been unable to contact her by phone.
"Her family and friends are becoming increasingly concerned for her wellbeing as it is out of character for her not to stay in contact.
"We are continuing to work with our colleagues in Tayside Division in our attempts to trace both Emma and her boyfriend, who has not been in contact with any of his family members either.
"They may be using a white Ford Ranger pick up truck with the registration number SJ51 YRM."
Anyone with any information should to contact Police Scotland on 101.