Markham's fiance, John Carter, did an interview with Grace over the phone. Carter was the last person to see Markham.
No one has seen Markham since Aug. 14.
Friends and family created a Facebook fan page called "Bring Katelyn Markham Home," where a flyer was featured offering $3,000 Monday, but was later increased to $5,000 Wednesday.
Detectives call this case unique because of "the fact that someone has literally just vanished without any indication as to where they would go or why they would go there or who would be involved in their disappearance," said Lt. Kevin Haddix on Aug. 17.
Police are asking anyone with information on her disappearance to call Crime Stoppers at (513) 352-3040.
To see a clip from the "Nancy Grace" show, click on the video player above.