A Louisville, Kentucky mother who dedicates her time volunteering for an organization that searches for missing people has vanished.

Andrea Michelle Knabel, 37, was last seen around 1 a.m. on August 13, 2019, walking in the area of the 4000 block of Fincastle Road near her home in Louisville’s Audubon Park neighborhood, Andrea’s sister, Erin Knabel told Dateline.

“We talk daily, or every other day,” said Erin, who lives a few blocks away from her sister.

Erin added that Andrea “was sad” the last time she her, but that it isn’t like her sister to just walk off without telling anyone.

“She always keeps in touch with all of us, especially her children,” Erin said. “Even if she's visiting friends.”

Andrea is a single mother of two boys, ages six and eight. Erin said her sister spends her free time cooking, and the two of them do yard work together and take their children swimming.

“She is caring and thoughtful to others to a fault,” Erin told Dateline. “She is a joy to be with and my life won't be the same until she's back.”

Erin said Andrea had been laid off from her job at Humana, and then she was involved in a hit-and-run accident earlier this year that totaled her car.

Since then, Andrea had been volunteering for the organization “Missing in America,” Erin said. The organization, which is unaffiliated with Dateline’s digital series, has one mission: to locate missing adults and children.

“Andrea is not only a member, she has searched for a lot of missing people. She’s also a very good friend,” Missing in America’s founder Nancy Schaefer said in a video posted on the Finding Andrea Facebook page.

According to Schaefer, volunteers from Missing in America have been coming in from all over the United States to assist with the search for Andrea.

“I’m not going to stop looking for her. She’s my best friend. She’s a lot of people’s best friend,” Schaefer said. “She’s one of our own and we’re going to fight for her. We’re going to find her.”

In another video posted to the Finding Andrea Facebook page on Friday, private investigator Tracy Leonard said he is working on Andrea’s case, along with the Louisville Metro Police Department.

"We are looking at a couple different avenues and checking leads out daily. We have no indication at this point that leads us to believe that there is any foul play, but we are still very early in our investigation," Leonard said. "… We're just going to continue to look at what facts we discover."

Andrea’s sister Erin told Dateline she is “worried someone took her who doesn’t care about her or that she is hurt,” but added she doesn’t know anyone who would want to harm Andrea.

Leonard said in the Facebook video that he did not want to disclose more details on why Andrea may have walked off in the early hours of August 13, but added that she “was pretty upset, pretty wound up when she left walking."

There were security cameras in the area, Leonard said, but “a lot of those cameras weren’t active.”

Leonard said Andrea made some phone calls between 1:30 a.m. and 2 a.m., in the area where she was last seen. She was asking for a ride, he said. But the cell phone has “not been active” since then and they have not been able to ping it.

The investigator said that Andrea has friends all over Louisville, parts of Southern Indiana and is a “very well-liked young lady.” He added that her children are the “limelight of her life.”

The Missing in America organization said Andrea is the first member of the group to have ever gone missing.

Andrea is described as a white female, 5 feet, 7 inches tall, approximately 190 pounds, with light brown hair. She was last seen wearing a light-colored tank top and white shorts.

Anyone with information on Andrea Knabel’s whereabouts is asked to contact investigator Tracy Leonard at 502-618-9337, investigator Dan Washington at 502-722-8181, Missing Person Recovery Specialist Nancy Schaefer Smith at 502-500-3026 or the Louisville Metro Police Department at 502-574-LMPD.