Police were called to an address in Holland Street at about 16:15 on Wednesday where they found the body of James Chadwick, who was from the city.
He had a number of unexplained injuries.
Following the results of a post-mortem examination, his death is now being treated as murder.
Officers have been carrying out door-to-door inquiries and reviewing CCTV images from the area.
Det Ch Insp Iain Smith, of Police Scotland, said: "This investigation is at an early stage and it is important we establish what has happened which led to James Chadwick losing his life.
"Our inquiries so far have established that Mr Chadwick was last seen on Monday 31 August and we're appealing to anyone who has any knowledge of his movements since 31 August to contact police as a matter of urgency."
A murder investigation has been launched following the death of a 37-year-old man in Aberdeen.