Antony Hill, who also uses the names Antony Richie and Antoine Richis, is believed to have been in Manchester city centre on Wednesday February 24.
Antony is described as a white male, 5ft 10ins tall of very slim build with short dark hair.
Detective Inspector David Shaw, from West Yorkshire Police, said: “We are growing increasingly concerned for Antony’s safety and welfare as it is out of character for him to go missing and to not be in contact with anyone.
“We believe that Antony was in the city centre of Manchester on February 24, and know that he has links across Greater Manchester and Lancashire, as well as in the upper valley area of Calderdale.
“I would appeal to anyone who has seen or heard from Anthony in the last month, or who knows where he is now to come forward. I would equally appeal directly to Antony to get in touch so we know that he is okay.”
Anyone who has seen or heard from Antony, or who knows where he is now is asked to contact Calderdale CID on 101.