In the original missing person notice, Allentown Police said the two might be traveling together in a red, two-door Honda Accord with the PA license plate KLT 0529. School records showed that 45-year-old Kevin Esterly repeatedly signed Amy of school in the months before their disappearance.
Captain Bill Lake said at the time Yu's mom made the initial report of her missing child to police March 5, around 6:30 p.m., Yu was on a flight with Esterly from Philadelphia to Dallas and to a final destination of Cancun, Mexico.
The teen's family previously said the two of them met at church years ago, and Amy is friends with one of Esterly's daughters.
Lake also said despite believing initially that Yu boarded her bus to Lee High Valley Academy Regional Charter School on the morning of March 5, that was not the case: "Through investigation, it was subsequently learned that Amy had never boarded her bus that morning". Police say the teen had changed school documents to list him as her stepfather.
Mexican authorities issued an Amber Alert and suggested that the pair could be traveling within the country.
Amy's mother Miu Luu made a plea for her daughter's safe return to CBS News earlier this month.
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February 9 was the final day because that's when Yu's mother came to the school to pick up her daughter, "and the school said her stepfather already signed her out of school", Hammer told ABC News last week.
Also, for the first time since her husband went missing, Esterly's wife gave a statement to the Morning Call on Friday, also pleading for the teen and Kevin Esterly to return home from Mexico. "Stacy did not believe it to be merely a father-daughter relationship, and that's why there were fights". The department found video of Esterly signing the teen out and leaving with her, Hammer said. According to ABC News, Esterly's wife claims he took out $4,000 from her bank account and that his vehicle and personal documents are missing.
"I want to tell her - Amy, can you come back to me?"
Esterly has a warrant out for his arrest on the charge of interfering with the custody of a child. Lake said authorities have received numerous tips as a result of media attention and asked the public to call in if they have any information.
"I want to tell her, 'Amy, can you come back to me?"