The parents of a Minnesota girl who has been missing for 25 years have been asked to leave their home while police and FBI agents who have reopened the cold case appear to be concentrating on the property.

Amy Sue Pagnac has been missing since 1989. Pagnac was 13-years-old when she was last seen in the passenger seat of her step-father's car at a gas station on Aug. 5. Police say he submitted the missing person report, telling police he went to use the bathroom, came out, and she was gone. Pagnac was never seen again, police said. Next month, she would be 38 years old.

Pagnac's parents' home is now the subject of the search. Maple Grove Police have asked the couple, Marshall Midden and Sue Pagnac, to leave for the time being.

Amy Sue Pagnac was last seen at this gas station, 25 years ago.

The girl's mother, Susan Pagnac, told ABC News today that the cops politely asked them to leave.

"They came in, they told us what they wanted to do, were very polite, very helpful. I have a broken foot, one even helped pack a luggage so I didn't have to lift a finger," she said. Police told her would likely have to stay away from her home for a week. She said cops did not tell her why they were at her house.

Susan Pagnac said she believes her daughter is still alive and cited the rescue last year of three women who had been held captive for a decade in a Cleveland, Ohio, house of horrors.

"There's never been a moment that we give up on her,… How do you do that? The worst thing is the concept that someone you know is a victim of trafficking, like that guy in Ohio having her. Those are very scary thoughts. But once they are found, those individuals will recover," Mrs. Pagnac said.

"We wonder if she still has a beautiful singing voice," she said.

Susan Pagnac said that on the day her daughter disappeared the two were planning to go shopping for school clothes.

"She told me not to get too active or overdue because we had a lot of shopping to do," Mrs. Pagnac said.

Police and FBI agents have brought in heavy machinery to aid the search for clues, authorities said.

"It's our mission to make sure she's brought home. Since the Maple Grove Police Department took this report in 1989, we have actively investigated this case. We have been following up on every lead. Part of the investigation is still ongoing. That is why we are here today," Maple Grove Police Captain Keith Terlinden said on Sunday.

According to ABC News Minnesota affiliate, KSTP, the search warrant in the case is sealed and no details will be made public while the investigation is underway. No one has been taken into custody and no suspects have been named.