Harley Taylor, 13, was last seen in the Harrison Road area of Chorley in the early hours of December 25.
Hi is described as white male, 4ft 1in tall, with light brown hair and of a slim build.
A spokesperson for Lancashire Police said: "We are becoming increasingly concerned about the welfare of 13-year-old Harley Taylor, who is missing from his home address in Darwen.
"Harley was last seen in the Harrison Road area of Chorley in the early hours of December 25, 2019.
"We are now concerned for his welfare and are appealing for your help to find Harley.
"Likewise, we would like to appeal directly to Harley – if you see this post please contact the police so we can check you are safe and well."