TILTON, Ga. — The disappearance of a Whitfield County teen still is a mystery as the search reaches day three today.

Whitfield County Sheriff Scott Chitwood and Emergency Services Director Jeff Putnam said Saturday evening that they don’t know what happened to 19-year-old Brett Andrew Thomason, but the possibility of a hoax has not been ruled out. Mr. Putnam said a faked disappearance is preferable to the alternatives.

“I’d love for him to come out of somebody’s house and say I’ve been hiding for whatever reason,” Mr. Putnam said.

The young man is enlisted in the Marines and is scheduled to leave for boot camp at Parris Island, S.C., in April. Friends and family said he was happy and proud to serve in the military and had no significant worries.

Mr. Thomason was last seen by two friends about 8:30 p.m. on Thursday during a trip down the Conasauga River in a flat-bottom aluminum boat.

Authorities found the boat on a river bank and found a wooden oar from the boat in a nearby field.

Searchers also discovered what might be a spot of blood bigger than a softball near a barbed-wire fence, and Mr. Putnam said that substance is being tested.

Sheriff Chitwood said all options are being considered in the disappearance, but investigators still are treating the situation as a search and rescue. They have not begun inquiries into whether or not Mr. Thomason may have used credit cards since Thursday.

Mr. Putnam said authorities are concentrating on a five-mile radius around the area where the boat was found.

Eight dogs trained to find humans and cadavers, and their handlers, led Saturday’s search effort.

Many family members, lacking sleep because of worry and private search efforts, waited for word on their loved one Saturday at the search’s central command center at Riverbend Baptist Church.

“We’ve still got hope because we don’t have a body,” said Mr. Thomason’s stepmother, Stephanie Thomason.