The search for 19-year-old Marty Stanaford and 20-year-old Cameron Buerger on Monday involved agencies in Ohio and Kentucky that were searching the river and riverbanks.
The two men, both from Troy, north of Dayton, set out Saturday from Levanna, about an hour upstream from Cincinnati.
The Ohio Department of Natural Resources, the Ohio State Highway Patrol, local authorities and friends and relatives of the two men have been searching since Sunday.
Authorities said they were traveling in a green, 15-foot canoe.
A cooler believed to be one they were carrying has been found at a dam.