"We are carrying out air and sea searches for the missing," Red Cross shift supervisor Alexander Morales said Sunday.
The body of Danielle Tongier, 18, who graduated from the school last year, was found Saturday, according to school authorities and Costa Rican officials.
Searchers on Sunday recovered the body of Andrew Harpstrite, a 17-year-old junior at Labette, said Red Cross guard chief Carlos Bolanos.
The two teens, along with junior Jessica Pierce, 17, apparently got in trouble while swimming off Palo Seco beach, near the town of Parrita, about 180 miles south of the Costa Rican capital of San Jose.
Brett Carlson, who taught Spanish at the school, reportedly jumped in to try to save them. Pierce and Carlson still were missing Sunday evening.
Labette County school Superintendent Dennis Wilson said that 10 students, Carlson and another chaperone had been in Costa Rica since June 6, and students saved money all year for the language and arts trip.
"It was kind of a highlight for those who were in Spanish II classes," Wilson said.
"Mr. Carlson was a very popular and well-liked teacher," he said. "We'll have counselors available this week at the school for students who want to come up and talk to people."
The group had been scheduled to return June 14.