His parents flew there to help in the search, along with the Red Cross and other volunteers.
Congressman Mark Kirk is suggesting sending a U.S. military plane equipped with an infrared camera to detect a human presence deep in the jungle.
"Time is not on our side, but I think if we can bring more assets to bear, we increase the chances of rescuing David," said Kirk.
Kirk is hoping to quickly get permission from Costa Rica's government to use that type of equipment in the jungle.
Relatives say Gimelfarb went to Central America to relax after the death of his grandmother.