CHICAGO (CBS) — Two months after their disabled 21-year-old daughter and 2-year-old grandson went missing, her parents have asked anyone who will listen for help in finding the pair.

Diamond Bynum and her nephew, King Walker, vanished on July 25, after going for a walk near their home in Gary, Indiana.

Bynum’s father, Eugene Bynum Jr., said it’s been a difficult two months. He believes his daughter and his grandson are still alive.

“If they weren’t alive, we would have came across some bodies; not just necessarily us, and our search team, or my family, but people who actually live in Gary,” he said. “In my heart, I do believe they’re alive.”

He and a handful of others have searched for his daughter and grandson every day, often searching abandoned buildings.

“There’s over 15,000 abandoned buildings in Gary. There’s just a handful of us,” he said.

He said he believes they are being held by someone. Why, he doesn’t know.

“Please let them go. We’re not concerned with pressing charges. We just want our family back,” he said.

Diamond Bynum’s mother, LaShann Walker, said several people have told her they believe they’ve seen her and her nephew in Chicago’s Roseland neighborhood, in the company of a woman.

“One was at the White Castles on 111th and Halsted; one at the Checkers on 115th and Halsted; one on 119th and Normal,” she said. “A couple – a guy and his wife – said they really strongly believe they are in the area.”

Diamond Bynum walks with a pronounced limp, and has very limited mental ability.

Police have said Bynum is developmentally disabled, and might have gotten lost while walking her nephew from their new home in Gary to a local store.

Bynum’s family moved to Gary from Hammond in February, and police have said she is not yet familiar with the area around her new home in the 500 block of Matthews Street.