Coast Guard helicopter crews at the heavily forested site were told by searchers late Tuesday that there were no survivors, Coast Guard Lt. j.g. George Adams said.
The single-engine floatplane, a de Havilland Beaver, had left Ketchikan shortly before 1:30 p.m. for a tour over Misty Fiords.
Alaska State Police said early Wednesday that pilot Joseph H. Campbell, 56, was flying the plane with cruise passengers William F. Eddy and Jeanne J. Eddy, both 59 and from Florida; and Paul J. McManus, 60, and Marianne M. McManus, 56, of Massachusetts.
A dispatcher for Taquan Air, the Ketchikan-based flight operator, reported the plane missing after trying to contact the pilot for 20 minutes without success, said Len Laurance, a Taquan spokesman.
Searchers spotted the wreckage in the area where an aircraft distress signal had been picked up, near the south arm of Rudyerd Bay about 35 miles northeast of Ketchikan.
The four passengers had been traveling on the Sun Princess, a Princess Cruise Lines ship that was on the second day of a seven-day trip from Seattle. The vessel left Ketchikan two hours after its scheduled departure of 4:30 p.m.
The cruise ship company, a division of Carnival Corp., has cut off Taquan Air tours at this time, Princess spokeswoman Julie Benson said in a prepared statement. Princess, based in Santa Clarita, California, also notified the families of the passengers.