Fifty Red Cross volunteers have been searching for him.
"Unfortunately, this is a really dense, forested area," said family friend Benjamin Dias. "So, it is really hard to cover much ground."
"We're working closely with the family to confirm any information we can and we'll be working with them to extend any assistance we can while they work to reunite with their son. He is a member of our student body, and we are very worried about him," said Jo Beth Cup of the Adler School of Professional Psychology.
Gimelfarb is a Highland Park, Ill. resident. His parents have flown to Costa Rica to join the search.