Nancy Ng hasn't been seen since Oct. 19, when she reportedly took a kayaking trip with others from the retreat.
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Her family has hired professionals to help with search-and-rescue efforts around Lake Atitlán.
But the leader of that effort says he is having trouble getting answers from witnesses - some of whom have since returned to Southern California - and he is suggesting there is a need for a criminal investigation into her disappearance.
The FBI and State Department have been in contact with Guatemalan authorities about the case.
Her family is just pleading for anyone with information to come forward.
"I miss my Nancy very much," said her mother, Stephanie Li. "And hope the government helps us find answers and bring her home."
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Nancy works for the Alhambra Unified School District. This was the second year that she went on the yoga trip.
Private crews have been scouring the area around the lake from the air and below the surface, but have not found any signs of Nancy.
A GoFundMe has been set up to help fund those search efforts.
The head of that effort told Eyewitness News the failure of potential witnesses to provide more information leads him to request criminal authorities get involved in the investigation.
Chris Sharpe with Guatemala-based Black Wolf Helicopters says he's searched most of the lake without any clues to Nancy's disappearance. At this point, he's starting to question if she even really went kayaking at the lake.
"For me, this is now becoming a criminal investigation because the witnesses who were there at a material time are not being forthcoming," Sharpe told Eyewitness News.
The family doesn't know why witnesses aren't being more cooperative.
"We're begging you: If anyone saw anything that could help us, just direct us where to look," said Nancy's sister, Nicky Ng. "Because we need answers."