The adoptive fathers of Harmony Montgomery's brother spoke Saturday on ABC's Good Morning America in hopes that someone will come forward with new information about the missing girl.Blair and Johnathon Miller said their adoptive son Jamison spent time in foster care with Harmony Montgomery, his biological sister.The Millers adopted 5-year-old Jamison out of foster care in Massachusetts when he was 3 years old."The first picture we ever got of Jamison was with his sister," Johnathon said. They said Jamison fondly remembers his sister in detail and wants to see her again."Jamison just talked about her and told us about her beautiful blond hair and her glasses and her blue eyes," Johnathan said. "He often asks about her. He looks for her at a park ... He misses his sister."The Millers said their family was once at a baseball game and Jamison did not want to leave because he thought he saw Harmony."He said, 'I think that's Harmony over there,' and he wanted to go play with that little girl just to make sure it was not his sister," Johnathan said. Johnathan said he cannot find the words to explain the current situation to his son."The thought that I may have to tell my 5-year-old that we could not protect your sister the way we get to protect you is heartbreaking," Johnathon said. Jamison's dads said they are in contact with Harmony's mother, Crystal Sorey. "Every time we look at him, we think 'what story are we going to tell Jamison? How is the story going to end?'" Blair said. "We are very optimistic and very hopeful that Jamison sees his sister again."The Millers said they are in constant communication with police and frequently send along any tips they receive to detectives. "She has a little brother that loves and needs her," Johnathan said. "He wants to hug his sister again, and we want to give him that opportunity."A reward for information regarding Harmony's whereabouts now sits at $137,000. Tips can be made to a dedicated hotline at 603-203-6060.