Larry Harvey of Kennesaw said he is offering $1,000 for information that leads to an arrest.
Boortz's announcement brings the reward total to $8,000 .
The horse is now recovering after surgery to remove the three arrows -- one that pierced the middle of its spine, an area below its eye and one that traveled through its neck, Fayette sheriff's investigator Brent Rowan said.
The nonprofit Georgia Outdoor Network is offering a $1,000 reward and the Atlanta Humane Society added $5,000 to the reward.
Rowan said someone was driving along Banks Town Road in Brooks on Sunday and spotted the horse with arrows sticking out of its body. Sheriff's deputies and a veterinarian responded, Rowan said.
The vet spent four hours working on Misty, and told WSB-TV the mare could still suffer from bone damage.
Neighbor Rachel Byrd told WSB she was driving by and spotted Misty standing on her owner's farm. She slowed down and noticed the arrows sticking out of her.
"She was scared to death. She wouldn't let us catch her. You could tell in her eyes that she was in a lot of pain, and she was very scared," Byrd told WSB.
--Staff Writer Ty Tagami contributed to this article.