Detectives are yet to locate the 25-year-old person of interest, Benjamin James Milward, who was seen in the Kurilpa Park area on the evening of March 27.

Ms Collombet's body was found in a rotunda at the South Brisbane park the following morning.

Witnesses have told detectives Mr Milward had been using drugs on March 27, although it wasn't clear what time he had used them or whether he was still under their influence by the evening.

Mr Milward was also captured on security footage earlier in the day at the Melbourne Hotel in South Brisbane.

Police are yet to find Mr Milward and have issued an Australia-wide alert to locate him. While he hasn't been declared a suspect by police, they have warned the public not to approach him.

Investigators spent the weekend door-knocking businesses in Bowen Hills, after security cameras captured footage of Mr Milward at the Bowen Hills train station about two hours after Ms Collombet's murder.

Mr Milward was seen leaving the train station at 11.35pm on March 27, having caught a train from South Brisbane 12 minutes earlier.

On Saturday, Inspector Rod Kemp said Mr Milward appeared “disoriented” in the footage.

He said police had no confirmed sightings of Mr Milward since that night, although Crime Stoppers had received “dozens” of calls.

His bank account has not been touched, and several of Mr Milward's family members have begged him to come forward.

“It's concerning that the longer it goes, the more suspicion's aroused with this person,” Inspector Kemp said.

He is described as Caucasian, about 180 centimetres tall, with short fair hair, hazel eyes, a proportionate build and a dragon tattoo on the left side of his chest.

Mr Milward was wearing a black singlet and long, black pants with sneakers.

Meanwhile, Sophie Collombet's heartbroken family have spoken about the loss of the 21-year-old, who was due to return home to France in June.

“We still can't believe it, we thought 'it can't be true, it's not true, it's not real' we still can't believe it has happened,” Ms Collombet's mother Corinne told News Corp.

The family is now penning a tribute to Sophie, which will be read out at a public vigil on Thursday.

Ms Collombet's brothers said their sister was an avid traveller and had enjoyed living in Australia.

“She would tell us how great it was in Brisbane. She was an adventurer, very curious and loved travelling. She had friends everywhere,” Guillaume Collombet said.

Anyone with information should contact Crime Stoppers on 1800 333 000.