Pheobe, 17, was last seen near Bundaberg airport in southern Queensland about 8.30am on May 15 after booking a trip to Western Australia to see her boyfriend.
CCTV footage indicated Pheobe never arrived at the airport terminal, police said.
Police on Wednesday said a man was assisting their investigation.
"A 34-year-old man has been taken into custody and is currently assisting police with enquiries as part of ongoing investigations into the disappearance of Pheobe Bishop," a statement said.
"No charges have been laid."
Police earlier on Wednesday said they had scaled back their search for Pheobe after weeks of combing the Gin Gin area where the teenager lived with two others on a property.
Pheobe's mother Kylie Johnson has been pleading for information since her daughter's disappearance, documenting her family's heartache on social media.
In her latest post Ms Johnson wondered if her life would ever be the same again.
"Starting day 20 with you still missing Pheobe," she posted on Facebook on Wednesday.
"I don't know if life will ever be the same again? I don't know if I will ever look at the world the same way that I did before May 15th.
"What I do know is that people have information on where you are Phee and we need that reported to police."
The search initially focused on Good Night Scrub national park, an hour's drive from the airport, with homicide detectives and police divers called in.
Some items believed to be linked to the investigation were seized for forensic examination.
The search also revealed evidence might have been moved from the national park before police arrived.
The search then focused on Gin Gin where Pheobe lived with two others at a property.
The property and a grey Hyundai ix35, thought to have been used to take the teen to the airport, were declared crime scenes.
Pheobe's housemates James Wood and Tanika Kristan Bromley have been charged with unrelated weapons offences.
Bromley was granted bail at Bundaberg Magistrates Court to reappear on June 23 while Wood was issued a notice to appear on June 13.
Police have said the weapons charges were unrelated to Pheobe's disappearance and there was no suggestion Bromley or Wood were involved.
Anyone with information, footage or sightings of the grey Hyundai between May 15 and May 18 in the Gin Gin area has been urged to contact police.
Pheobe is about 180cm tall with a pale complexion, long hair that has been dyed red and hazel eyes.
She was last seen carrying luggage, wearing a green tank top and grey sweatpants.
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