"Words can not express the devastation within her family and friends", her relatives said in a statement. It was the last time that her family would hear from her.
According to its listing on TripAdvisor, the Villa le Mas is a compound with seven vacation apartments.
Authorities believe it was Stefaniak but have not officially identified the remains, they have said.
Late Tuesday, in an emotional Facebook post, her family said that Stefaniak's father had confirmed the body found was his daughter's.
"'I'm just gonna go ask the guards to buy me a bottle of water.' He says that her phone died, and that's it", Burton recalled, adding: "That's the last we heard from her".
Her body was found by cadaver dogs on Monday partially buried in the ground and covered with plastic bags behind the apartment complex that housed her Airbnb.
"Words can not express the devastation within her family and friends", the post said. "We want the world to know that we will never forget Carla", a Facebook post on the Finding Carla page said.
"It's too much for us", her father, Carlos Stefaniak, told ABC Action News in Tampa from Costa Rica.
Costa Rica's Judicial Investigation Department General Director Walter Espinoza said they're looking for clues including where Stefaniak's belongings are. Pictured above is the AirBnb rental where she was staying.
An autopsy on Stefaniak showed multiple stab wounds to the "neck and upper extremities", as well as blunt force trauma to the head, the spokesman said.
Investigators found blood inside the Airbnb where she was staying.
A suspect, Bismarck Espinoza Martinez, 32, is in custody in the case, officials said Tuesday during a news conference. "We know she was abducted".
The owner of the Airbnb told relatives she was seen entering an Uber with her luggage around 5 a.m. Wednesday, but Uber records do not show a transaction.
An Airbnb representative said the company is cooperating with local authorities in Costa Rica.
On Nov. 28 - her birthday - Stefaniak did not board her scheduled flight home and family members grew anxious when she didn't respond to messages wishing her a happy birthday.
An Uber driver who took Stefaniak sightseeing on the Tuesday and who was supposed to pick her up to go to the airport told the family he heard she left the rental home around 5am with her luggage and got into a mysterious vehicle, according to the Miami Herald.
April Burton, her sister-in-law, told CNN the two had gone to Costa Rica to celebrate Stefaniak's birthday and had traveled together for six days, staying in beach towns outside San Jose. Stefaniak never made that flight. Stefaniak also failed to respond to a number of birthday messages from family and friends. He said Carla was a "happy soul" who made everyone laugh and had a large social media presence.
Stefaniak, who was an insurance agent, loved to travel and post photos on Instagram. It featured her in a turquoise bathing suit, lying near a pool with tropical plants in the background. "I'm going to miss the place", she wrote.