Kevin Bishop, 32, was reported missing in Paisley on August 4 after his family had not heard from him.
A search was launched and the last confirmed sighting of Mr Bishop was found to have been in Well Street, Paisley, on July 27.
Police said the 32-year-old has never been missing before.
He is white, around 6ft 2in with a slim build and brown hair. He also has “Kevin” tattooed on the back of his neck.
Chief Inspector Alison Kennedy said: “As time goes on, we are growing increasingly concerned for Kevin. There has been no further confirmed sightings of him since Friday 27 July 2018.
“He has never been reported missing before and it is out of character for him not to keep in contact with his family and friends.
“If Kevin sees this appeal I would urge him to contact his family or the Police directly.
“We urge you to think back, where were you that Friday, or have you seen or heard from Kevin since then? Please come forward, we need to make sure he is safe and well.”