Lewis Connoly, 17, was last seen at Buckshaw Train Station boarding a train destined for Manchester at 5.50pm on January 2.
A spokesperson for Lancashire Police said: "We are becoming increasingly concerned about the welfare of year 17-year-old Lewis Connoly, who is missing from their home address in Buckshaw Village.
"We are now concerned for their welfare and are appealing for your help to find Lewis.
"Likewise, we would like to appeal directly to Lewis should he see this post, please contact us so we can make sure you are safe."
Lewis is described as a white male, 5ft 7in tall, with blonde hair and of a slim build.
He was last seen wearing black tracksuit pants, a black hoodie and black Nike trainers.
If you have seen Lewis or have any information, please call police on 101 quoting log reference LC-20200102-1075.