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NASHVILLE (CBSMiami) – A nationwide manhunt is underway for a former Tennessee teacher accused of convincing a teen student to run away with him.

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Investigators believe 50-year-old Tad Cummins kidnapped 15-year-old Elizabeth Thomas.

Cummins was fired from his teaching job last week over allegedly inappropriate behavior with the teen. He faces charges of sexual contact with a minor and aggravated kidnapping.

On the day Thomas disappeared, both wrote cryptic messages on Instagram. Cummins posted “Let’s do this.”

Thomas brother James said this turn of events has devastated their family and he would like for Cummins to do what’s right.

“Even if he doesn’t go with her – if he could leave her somewhere safe and let the police know where she is, so we can have her, if he can just drop her in a public place and say hey, here she is,” said Thomas

On the morning of March 13th, a friend dropped Thomas off at a Shoney’s restaurant in Columbia, Tennessee. About eight hours later, information obtained by the Tennessee Bureau of Investigations placed her about 70 miles away in Decatur, Alabama.

Surveillance video appears to show Cummins putting gas in his silver Nissan before allegedly meeting up with Thomas on the morning she disappeared.

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“We honestly have no idea where these two individuals are right now,” said Josh Devine, with the Tennessee Bureau of Investigations.

Despite Amber Alerts in Tennessee and Alabama, Devine said they’re not getting the influx of tips they need.

“Either they’re off the grid, so they’re outside the view of the general public, or they’re outside our original concentration area here in the southeast,” said Devine.

Cummins worked at Central Tennessee High School where Thomas is a freshman.

In a letter to the Maury County School District, Thomas family attorney Jason Whatley claimed another student saw Cummins kissing Thomas in January. The school district said they “suspended” Cummins when they “were notified of the allegations.” But Whatley said the school waited more than a week to take action.

“Any suggestion that he was suspended immediately when these allegations came out is just false,” said Whatley.

“My heart breaks for the family of Beth Thomas,” said Cummins’ wife Jill who begged her husband to come home over the weekend. “This is not who you are. We can help you get through this.”

Devine said even though it has been a week, they remain hopeful.

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“You have to be optimistic,” he said. “The mission of our agency is to find him, make sure he’s in custody, and bring her home.”