Pearce was last seen in Modesto, California on April 21, 2005. He was scheduled to volunteer at Woodland Elementary School and Mariposa Middle School the following day, but never arrived at either place. He has never been heard from again.

A few days after Pearce's disappearance, his 1990s model Ford Ranger pickup truck was found stuck in mud and burned on Chowchilla Mountain Road above Ponderosa Basin near Summit Camp in Mariposa County, California. There was no sign of him at the scene. Authorities stated it appeared the vehicle had caught fire accidentally, and they theorized that Pearce became lost when he tried to walk out of the mountains after abandoning his car. There is no evidence to support any theory, however, and no possibilities are being ruled out.

Pearce is described as a dedicated school volunteer who was popular with the students and often worked a 50- to 60-hour schedule. He is a retired nuclear and chemical engineer. He was in good health at the time of his disappearance and was not exhibiting symptoms of confusion or memory loss. Pearce's case remains unsolved.