Authorities on Monday expanded the search for a missing four-year-old boy.

Henry County authorities said 4-year-old David Tippin (search) slipped out the back door of his home early Sunday morning and has not been seen since.

His parents last saw him at 2 a.m. Sunday. They called police Sunday morning when they awoke to go to church and the boy was gone, authorities said.

Dozens of volunteers broadened the search beyond the half-mile radius they had already covered, but the process has been slowed by the terrain, police said.

"There are areas of very heavy undergrowth that must be searched manually," said Lt. Kenneth Turner of the Henry County (search) police. "There are also areas out there that are unpopulated, and we're having to manually search those areas. We're trying to be methodical."

The boy has dark brown hair and brown eyes. He has a slim build and was wearing an electric blue "Finding Nemo" T-shirt and gray shorts.

Authorities set up a command post at Faith Baptist Church (search), which the boy's family attends.