On October 24, 2015, 18-year-old Little Rock native Ebby Steppach made plans to meet her stepfather, Michael, but she never showed up. The next day, she had a phone conversation with her older brother in which he described her as disoriented, and that was the last time anyone heard from her.

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Her mother, Laurie, and Michael say in the weeks leading up to her disappearance, Ebby’s behavior changed “drastically.” They say she would lie about her whereabouts and that she was provoking arguments.

But Michael says that it was an alleged incident at a party a few days before she disappeared that is most troubling.

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“Ebby [texted] me on Saturday, October 24, that she needed to speak to me about something important. She indicated that an individual at this house had sexually assaulted her and videotaped it,” Michael says. “The last question I asked her was if she wanted to go file a police report, and she stated, ‘Yes, I’m certain.’”

The parents wonder if Ebby’s stated desire to file a police report may have triggered her disappearance.

“I would like the four individuals that were at that party that evening with my daughter to come forward and give a formal interview with Little Rock Police Department to either help them move forward in the investigation, clear their name or help determine what happened to Ebby,” Laurie says.

WATCH: Why Mom Believes Missing Daughter May Have Been Sold Into Sex Trafficking

Do Laurie and Mike believe Ebby is still alive? On Friday's episode of Dr. Phil, hear about Ebby’s last phone conversation with her brother, and what police found inside the teen’s car that made her mother panic. Check here to see where you can watch.

If you’ve seen Ebby Steppach, call Detective Tommy Hudson at the Little Rock Police Department at (501) 404-3128. Or, call the Little Rock tip line: (501) 371-4660 or the Halos Investigations: (662) 420-6518.

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