(CBS) -- Carla Stefaniak was all smiles posting multiple videos and photos on social media as she and her sister-in-law, April Burton, spent a week-long vacation in Costa Rica.
"It seemed so safe when we were there, everything was great," said Burton.
Because of a prior commitment, Burton left Costa Rica on November 27th, the day before Stefaniak was scheduled to fly home. Now on her own, Stefaniak took an uber to her Airbnb, then had her driver give her a tour of San Jose. After returning around 5 pm, she told a friend it was "raining crazy" and the power was out. She said "It's pretty sketchy here." At 9 p.m. that night, all communication stopped.
That was highly unusual, according to her brother Carlos Caicedo, who spoke to us from Costa Rica where he's joined the search efforts.
"It was her birthday and she loves to be on social media. So I'm guessing every single app that there is that you can communicate, I'm sure she was on it," he said.
Caicedo says according to the owner of the Airbnb, a security guard saw his sister get into a car with her bags at 5 a.m. the next morning.
"...which makes no sense because her flight was at 1:30, and she was only 20 to 30 minutes away from the airport. And she is never early for anything," Burton said.
Adding to the mystery, the family says Stefaniak had checked-in online for her flight and ordered an uber to pick her up later that morning.
CBS News has contacted the U.S. embassy in Costa Rica and law enforcement there, but we've yet to hear back. Airbnb had no comment, and Uber says it will assist in the investigation.