Jessie M. Davis was reported missing June 15 when her mother found her 2-year-old son alone in her apartment, the Canton (Ohio) Repository reported.
On Thursday, FBI agents sifted through a 3-foot by 6-foot patch of freshly turned soil that had the appearance of a newly dug grave. The find turned out to be a newly planted marijuana patch, the Repository reported.
"It's very frustrating but we can't leave any stone unturned," Stark County, Ohio, Sheriff's Capt. Gary Shankle told the newspaper.
Also Thursday, close to 1,800 volunteers spent seven hours combing 9-square-miles of Lake Township, the Repository said.
"We're doing everything right," Tim Miller, founder of Texas EquuSearch, which Davis' family brought in to help with the search. "We just haven't hit the right spot."
He said he hoped weather would permit an unmanned aircraft to join the search Friday by taking hundreds of aerial photos.