David Douglas Boone, 56, was last seen at his Lake Forest, California, home on December 5, 2006, around 3:00 p.m. He left behind his vehicle, credit cards, identification, phone and cash while he was going through a divorce and under personal stress. His teenage son reported him missing the next day.

Bloodhounds followed Boone’s scent to Whiting Ranch Wilderness Park, a nearby popular hiking area, and authorities believe he may have gone hiking that afternoon. An extensive search of the park — including air support and rescue teams — found no sign of him. The official search ended after one week, with concern that Boone might not have survived cold conditions if injured or lost.

Boone was a golf club designer known for work such as the Parallax irons. His whereabouts remain unknown and the case is unsolved. Anyone who was in or near Whiting Ranch on December 5, 2006, or has information about his movements that day is asked to come forward.