Volunteers and law enforcement personnel have canvassed jungles of Saipan and combed through dirt and trash in search of two young sisters, who authorities believe were most likely abducted while waiting for the school bus three weeks ago. Meanwhile the reward fund has grown to about $33,000.

The FBI interviewed the girls’ father, Ruhtik Luhk, of Pohnpei, at the U.S. Embassy there this week after federal officials made a diplomatic request to the Federated States of Micronesia. The FBI is confident that Luhk is not involved in the disappearance and that the sisters are not on Pohnpei.

“We’re comfortable with the answers we got from the father,” FBI Special Agent Tom Simon of the Honolulu division said in a telephone interview from Saipan.

Faloma Luhk, 10, and Maleina Luhk, 9, were reported missing by their grandparents when they didn’t come home May 25. They were last seen waiting at a school bus stop that’s just 300 feet from their home. They never made it to Kagman Elementary.

“It’s just very hard not to know where they are now or their condition. It’s very terrifying,” their grandfather Elbert Quitugua told The Associated Press.

The disappearance of two girls from the small, close-knit island soon sparked a massive search effort involving local authorities from the U.S. Commonwealth of the Northern Mariana Islands, the FBI and volunteers. The island has a population of about 60,000 and while there is a crystal meth problem, there is a very low violent crime rate, Simon said.

About 100 searchers have joined in the effort. A local running group that usually jogs through the jungle has altered routes to go from abandoned building to abandoned building.

“We just can’t imagine how to thank everyone. There’s so much they’re doing for us to find our two girls,” Quitugua said.

Quitugua has been raising the girls for about three years because their mother works on Guam, where she has been helping with a family catering business and trying to find a better job. The girls’ parents met while training to be correction officers and their father moved to Micronesia after the relationship ended, Quitugua said. Their mother returned to Saipan after the girls were reported missing.

About 40 extended family members live in a group of houses in the village of As Teo next to a Santa Lourdes shrine. Quitugua said the Catholic family has spent their days praying and cooking meals for those helping with the search.

The girls come from a modest family, Quitugua said, describing how he and his wife sell shaved ice and smoothies once a week at a street market.

Local businesses, authorities, friends and family have contributed to a reward fund that has grown to about $33,000, he said.

The disappearance is the talk of the island and theories abound. Quitugua said he’s been told someone heard a car door slam near the bus stop where the girls were last seen, leading him to believe they rode away with someone they recognized. “Or else, why wouldn’t they scream?” he asked. “It’s something that’s puzzling to us.”

After a weeklong dig of the island’s landfill, authorities gave Quitugua four backpacks to identify, out of hundreds that were found. None belonged to the girls.

Searching on a small island is proving to be both challenging and beneficial, Simon said, noting that it’s not possible to drive very far, but the vast ocean “could mean you would never see them again.”