Mr Wright had a stroke which left him weak on his right side, his father said.
"He couldn't have put up a fight."
Police said forensic evidence at Mr Wright's flat in Caroline Rd, Mayfair, showed something may have happened to him at the address, and police were treating the investigation as a homicide.
He last spoke to a friend on June 21, and has not been seen since.
But this morning the national plea for information had not turned up any substantial leads for police, who were monitoring phone lines until 10pm last night.
"I am still waiting to hear back from the man who was running the phones, but I asked him to call me if there was anything of interest," Detective Sergeant Brent Greville said.
"Sometimes these things take time to play on people's consciences."
The Police Ten-7 programme, fronted by retired Detective Inspector Graham Bell, was called in after the search for Mr Wright went cold.
"[The show was] just mainly to generate people's interest and make sure they don't forget about Johnny," Mr Greville said.
"I am confident that we will find him."
Mr Wright is described as a caucasian with collar-length fair hair, who often wore a maroon Queensland rugby league jersey.