Forty-three-year-old Sherry Arnold was last seen at 6:30 a.m. Saturday in Sidney.
More than 200 people participated in a search Saturday that yielded a shoe believed to belong to Arnold's near one of her regular routes.
Assistant Police Chief Bob Burnison says authorities had to turn away hundreds of volunteers who wanted to help search on Sunday. National Guard troops, a helicopter, several airplanes and three dog teams also were involved.
Arnold has taught math in Sidney for 18 years.
Burnison says Arnold's disappearance is hard on the community, which lost 46-year-old firefighter Jody Ray Verhasselt in an avalanche near Cooke City on New Year's Eve. Sidney has about 5,000 residents.
