After nearly three weeks of looking, the Costa Rican Red Cross has suspended its search for David Gimelfarb, the missing 28-year-old Chicago doctoral student.

National and local Red Cross teams retreated from Rincón de la Vieja National Park on Friday afternoon having found no signs of Gimelfarb.

Freddy Román, a press officer for the Red Cross, said the search lasted longer than normal.

“Usually, we leave the search after eight days if we don't find anything because of the high costs,” he said. “But because of the support and help from the family, the U.S. embassy and some private companies, we were able to extend the search to 15 days.”

Friends and family of Gimelfarb began raising funds to aid rescue efforts shortly after the search began Aug. 12. Some of Gimelfarb's co-workers joined his parents in Costa Rica to pass out missing person flyers and run supplies to search teams that were camped out inside the park.

The family hired ResQglobal, a private, U.K.-based search and rescue company to help coordinate missions.

The U.S. government brought in two Blackhawk helicopters to Costa Rica to search for Gimelfarb with infrared technology.

Both the Blackhawks and ResQglobal have since left the country.

Park rangers and local residents are still helping the family search for Gimlfarb. Friends of the family said Gimelfarb's parents might hire a private investigator to help search for their son.

In Chicago, friends hosted an open-mic event on Tuesday night at Dollop Coffee and Tea, a coffee house on the city's north side, to show their appreciation for Gimelfarb's love of the arts. Friends said the coffee shop was one of Gimelfarb's favorite hangouts.