Homicide detectives found the blood during a search of a Bankstown unit several months after Minh Phuoc Nguyen, also known as Paul Nguyen, went missing on May 1, 2014.

Police believe the 50-year-old, may have travelled to a Dudley Street unit after answering several distressing phone calls and telling family he needed to sort out a "complication" with a business associate.

Fairfax Media has previously reported that police believe the Vietnamese businessman may have been associating with the same criminal underworld figures that have been linked to slain drug dealer Jamie Gao and a high roller who was shot outside McDonald's in Sydney's inner west.

On Tuesday Detective Inspector Jason Dickinson said police had also seized a white Pantech truck they believe was parked outside the Bankstown unit where police had located the large blood stain.

Police also conducted a search of the Georges River at Lansvale but failed to find any evidence linked to the suspected murder.

"Detectives conducted a crime scene warrant at that property earlier this year, locating a large blood stain on the carpet. While not yet confirmed, we believe the blood could be his," Inspector Dickinson said.

Police believe Mr Nguyen may have been targeted because of his links to organised crime but said they have failed to find any trace of his body or the brown metallic Renault Latitude rental car he was seen leaving in from the Sydney Hilton Hotel in George Street.

Three days after his disappearance, a group of cannabis-smoking men unwittingly gave police a few extra clues.

Police said the group set off the fire alarms at the Fountainbleu Motel Casula on the Hume Highway after smoking heavily inside.

In the corner of the room was a bin that contained the rental car agreement belonging to Mr Nguyen, an empty mobile phone box and the stub of a boarding pass, police said.

Police also seized a number of business cards that belonged to Mr Nguyen's friends and associates.

Mr Nguyen's brother, Tony Nguyen, has told Fairfax Media the  businessman acted strangely in the lead-up to his disappearance.

"He handed my sister-in-law's passport back to her that night and said, 'I'm meeting up with someone and it could be complicated'."

Tony Nguyen said Mr Nguyen was a loving father and successful businessman who recently sold two Baker's Delight stores at Carlingford; a Bread Top shop at Chatswood and a Parramatta pizzeria.

"It's pretty tough for my whole family and we've been so close together as brothers and I'm finding it very, very hard to cope," he said.

"Everyone in the family is just puzzled and we just don't know where or why."

Police said they also believed Mr Nguyen spent a lot of time at the Bankstown Sports Club and Oscars at Bankstown.

Anyone one with information about Mr Nguyen's disappearance on May 1 are urged to contact Crime Stoppers on 1800 333 000.