Members of the Revolutionary Armed Forces of Colombia, or FARC, snatched the hikers near a historic jungle city built around 500 B.C., police said.
The tourists were believed to be from Israel, Germany and England.
The Colombian government dispatched a rescue team.
The hikers were in a dangerous area fought over by Marxist guerrillas, right-wing paramilitaries and drug traffickers, said Jeremy McDermott of the BBC.
Colombia averages one kidnapping every four hours. And most are carried out by FARC, the BBC said. The group uses ransoms to fund its 39-year war on the state.
FARC also has many political prisoners, including former presidential candidate Ingrid Betancourt and three U.S. military contractors. FARC has been trying to trade them for rebels in Colombian jails.