Teen warned family to call police if she didn't come home, hours before she vanished.

One of the last conversations missing American teen Mary “Elizabeth” Thomas had with her family contained a chilling warning.

“She confided in one of her siblings that if she was not back by 6pm that day and she was to disappear, to call the police,” attorney Jason Whatley told People.

The 15-year-old has not been seen since.

Police in south-eastern USA are desperately searching for the Tennessee teenager who they believe may have been abducted by Tad Cummins, a 50-year-old health science teacher at her Culleoka high school.

A warrant has been issued for the teacher's arrest on charges of aggravated kidnapping and sexual contact with a minor, according to the Tennessee Bureau for Investigation.

The latter charge relates to an alleged incident involving Thomas that occurred on school property in January.

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Thomas was reported missing in Maury County on the afternoon of March 13, roughly five hours after she asked a friend to drop her off at a local restaurant.

It's alleged Cummins, who police have identified as "armed and dangerous", picked her up from the restaurant car park before both vanished.

Thomas was placed in the neighbouring state of Alabama last week, however Tennessee authorities say investigators are now light on quality leads.

“It’s been a week, and anything is possible,” Tennessee Bureau of Investigation spokesman Josh DeVine told People. “They might have changed their appearance or changed their vehicle. We’re trying to cast the widest net possible.”

Meanwhile, Cummins' wife has issued an emotional public plea to the 50-year-old, urging him to return the student safely.

"Tad, this is not you. This is not who you are. We can help you get through this," Jill Cummins told a press conference according to Fox-17 Nashville.

"Your family wants their Papi back. Please do the right thing, and turn yourself into the police and bring Beth home.”