"Very long days. Not much sleep and a lot of long hours searching for clues or following up leads." That is how Neill Blake describes her days now, in the two-plus weeks since she last spoke to her son.

"It's been the hardest thing I've ever gone through," she tells WSB Radio.

It was March 7 Blake was last with her 25-year-old son David, when the two of them attended the music recital of his Georgia State University roommate. When he walked her back to her car, he told her "Goodbye mom, I love you." By March 9, he had been reported missing. David's car was found at Kennesaw Mountain National Battlefield Park, in the overflow parking lot on Old Highway 41. The keys were inside, and so was a bag the avid hiker would often take on long excursions outdoors.

In the days that followed, there were a number of searches at or near the park involving Cobb County authorities and dozens of volunteers.  All came up empty.

Authorities have pulled back until new leads appear, so now Neill Blake says the family will be hiring a private investigator. And just this week, she traveled to the north Georgia mountains, to areas David often frequents. To "ask hikers if they have seen David, showing them a flier, also posting fliers wherever we can," she said.

Blake says of conversations she's had with people who know her son best, "very good friends, but not that many of them. He's the type of person who will form a deep friendship, and not a lot of superficial ones." All of them are at a loss as to what might have happened.

She has two other sons. One of them has started a GoFundMe page to help with the search efforts.

"The way I've been dealing with it, besides trying to expend a lot of energy hiking and showing the flier around, is just relying on my faith," Neill Blake says. And a wide network of friends who have supported the family greatly she adds.

"None of us can figure out where he went, or why."