Police said the man, described as 60 years old and weighing 160 pounds, was seen several times on New Year's Day with Meredith Emerson, 24, a Colorado native now living in Buford, Ga.
Union County investigator Kimberly Verdone said witnesses said the man had a yellow backpack with enough gear for days. She said they described the man as "weathered and no teeth."
Officials said Thursday that they believe the man was Gary Michael Hilton of DeKalb County. They said it was possible he was driving a 2000-01 white Chevy Astro van.
Friends said Ms. Emerson went hiking with her black Labrador retriever on Tuesday.
Her 1995 Chevrolet Cavalier was found abandoned Wednesday at the base of Blood Mountain.
Police confirmed that a water bottle and dog collar found near a hiking trail belonged to her.
At the request of the Union County Sheriff's Department, the Georgia Bureau of Investigation sent four agents to join in the search Thursday morning, GBI spokesman John Bankhead said. The Georgia State Patrol pitched in with a helicopter.
"She's an experienced hiker and a blue belt in martial arts," said Julia Karrenbauer, Ms. Emerson's roommate. "She's athletic and has a good head on her shoulders. So we're just hoping for the best."