The Belgian Malinois, named Trapper, has been missing near El Capitan Mountain since Sunday night.
"It's killing me … it's been three days now," said owner Rory Cameron.
Cameron and his 55-pound, 14-month-old Belgian Malinois were working their way down the base of the El Cajon Mountain hiking trail when they became separated.
"We were about 300 yards from the road … he just disappeared without a sound and that's very uncharacteristic of him," said Cameron.
He then waited five minutes, then 10 minutes, then two hours and then overnight: still no Trapper.
"He just never showed up," said Cameron. "I kept expecting him to come out of the bushes."
Cameron says he has retraced his steps every day since Trapper disappeared.
"He's used to the mountains," Cameron said. "He's been raised in the Sierras around the Tahoe Basin. The only thing that bothers me is if he did get hurt or hurt himself, he can't defend himself against a bunch of coyotes or mountain lions."
On Wednesday, Cameron and his friend Scott Craddock were armed with a new plan: they were going to put down bundles of clothes that smell like Cameron so that Trapper could possibly come back to the last place he saw his owner.
"I've got the shirt that I was wearing that day when we were working and another shirt that I wear often times when I work," added Cameron. "We're going to put those out where we last saw him around other areas of the trail."
He adds that he is going to keep searching until his canine buddy is found.
"He means the world to so many people and I don't know what I am going to do without him," said Cameron.
Cameron says that he has also been training Trapper to be his girlfriend's service dog, since she has lost her sense of smell.
He is offering a reward to anyone who finds his dog.