Nearly 600 volunteers worked alongside trained professionals Wednesday, but there was no sign of the missing child.
Their efforts were made difficult by cold temperatures and rugged terrain.
"The terrain was woods. It was thick in places," said Max Dudley, a volunteer. "Some places it wasn't that thick, but we took our time and you see the next person, and you look and you look and you look."
TIMELINE: All we know about Casey Lynn Hathaway's disappearance
Those factors added to the potential for dangerous weather, caused officials to only allow professionals to search on Thursday.
Craven County Sheriff Chip Hughes said Casey was playing with two other relatives, also children, in his grandmother's backyard Tuesday, but didn't come inside with them.
Officials said the grandmother and others searched for Casey for 45 minutes before calling 911.
"It's heartbreaking. I have two children so I can only imagine what the family is going through and we're a small community so you don't really expect anything bad to happen here," said Jonathan Ipock, youth pastor of New Haven Church.
Ipock said some of Casey's family attends his church.
"You have so many people volunteering from our community and surrounding areas because they were putting themselves in the shoes of the family," Ipock said. "What would happen if that was one of their children? It's just amazing to see everyone come together to help."
Hughes said his deputies have not ruled out any possibilities in the boy's disappearance, including "abduction or kidnapping." He said they're treating this as a missing child investigation and search.
The area that is being searched is extremely rugged, Hughes said Wednesday afternoon. The family has been cooperating fully, Hughes added.
The FBI, state investigators, and even Marines have joined the effort to find Casey. The Highway Patrol assisted on the ground and in the air.
People from as far as Wilmington and Kill Devil Hills came to join the search.
Temperatures were below freezing for six hours overnight in the Craven County area, according to National Weather Service data.
Hughes said Casey wasn't adequately dressed for the weather and he's concerned about sinkholes and deep water ditches in the area. He said divers are assessing nearby ponds.
Casey is 2'4", weighs 25 pounds, has strawberry blonde hair, and brown eyes.
He was last seen wearing a blue coat and dark-colored pants.
"We went through the woods - through the thicket and the briars," said volunteer Donna Harris, a mother of three. "We did it for three-and-a-half, four hours and it was bad. It was really bad out there. If everybody could come and help look for him, it would help. As it got darker, it was scary out there. I just can't imagine a 3-year-old being out there."
Anyone with information should call (252) 633-0498 or the NC State Bureau of Investigation at (919) 662-4500.