Disappearance of Dennis Martin
Dennis Lloyd Martin (born June 20, 1962) was an American child who disappeared on June 14, 1969, in the Great Smoky Mountains National Park in Tennessee at the age of six, six days before his seventh birthday. The search effort was the most extensive in the park's history, involving approximately 1,400 searchers and a 56-square-mile (150 km2) area.
Source: Wikipedia — Disappearance of Dennis Martin (CC BY-SA 4.0)