Police say it is now six days since 26-year-old Joseph Gallagher was last seen in his hometown at around 2am on Wednesday, September 1.
Joseph's family are becoming "increasingly concerned" for his welfare and police are now seeking the public's help to establish his whereabouts.
He is described as 6ft tall with a slim build and short, brown hair. He also has a distinctive tattoo on the left side of his chest.
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It is unknown what he was last wearing, but his family say Joseph normally wears tight tracksuit tops and bottoms.
As well as his hometown of Chorley, the 26-year-old also has connections to Morecambe, Lancaster and Blackpool.
"We are now concerned for Joseph's welfare and are appealing for your help to find him," said a spokesman for Lancashire Police.
"If you have seen Joseph or have any information, please call us on 101 quoting investigation number 04/142181/21.
"Please share this post and thanks for your help."