Detectives who are searching for a missing American beauty queen after she moved to Australia are digging up the garden of her ex-boyfriend's home.

Priscilla Brooten, 46, was last seen in Bracken Ridge, Brisbane in July 2018 but wasn't reported missing until December.

Excavators have dug two pits over a four-day investigation and are searching for evidence relating to her suspected murder that may have been buried.

Her ex-boyfriend Mark Waden, 42, was taken into custody after he was allegedly spotted digging near his front yard but has been released by police without charge.

Police believe Ms Brooten (left) was murdered. Mark Waden (right), 42, was arrested on Saturday after police received a tip from neighbours but has since been released

Detectives who are searching for a missing American beauty queen after she moved to Australia have continued to dig through the yard of her ex-boyfriend's home

Excavators have dug two pits and are now in the process of sieving through collected soil to gather anymore evidence relating to her suspected homicide

'All this will add to an overall reconstruction, expert opinion on what may or may have not occurred at this location,' Sergeant Mandy Watene said.

Ms Watene said both the front and back yard were to be searched, as well as inside the house.

Ms Brooten and her ex-partner were in a de facto relationship for a year before she disappeared.

Police believe Ms Brooten was murdered.

'We share the fear of Ms Brooten's family and friends and have reason to believe she may have met with foul play,' Detective Senior Sergeant Michael Hogan said.

Her blue Volkswagon Golf with plate number 875VXA was found abandoned in the same month she disappeared in Bunton Street, Scarborough about 9pm on July 6.

The 46-year-old, who studied literature, has not been in contact with friends and family since she went missing.

She occasionally instructed Zumba classes at Deagon's HealthWorks gym and attended a book club at Bracken Ridge.

Her daughter Caity Brooten, 22, said her mother was a beautiful person and moved to Australia six years ago 'because she did not want to get tied down' in the United States.

Police who believe Ms Brooten was murdered, have already dug up a narrow strip of a yard along the driveway looking for her remains