Robert McKenzie went missing from Gourock yesterday.
He is described as 5ft 2in with a slim build, short sandy coloured hair and blue eyes.
He was wearing a blue Adidas tracksuit and white Adidas trainers.
Police officers in Greenock took to social networks today in a bid to trace him.
A spokeswoman for Police Scotland said: "Police are concerned for the welfare of 15-year-old Robert McKenzie who has been missing from his home address in Gourock since 6.50pm on Thursday April 10, 2014."
Anyone with information is asked to contact Greenock Police on 101.