ALLENTOWN, Pa. - Amy Yu just turned 16 in December.
"She was like a pretty, beautiful sister," John Yu says, adding, "She always helps me and takes care of me."
Her younger brother John spoke with us alongside his mother, Mul Luu, who is Chinese and speaks broken English.
They say Amy was beloved in school, with lots of friends but Monday, after their mother dropped off John and Amy at the bus, John says Amy disappeared.
"She left," John says. "She just walked out, and went somewhere," he adds.
Back at home, Mul Luu discovered her passport was missing, along with cash.
John tells us, "I felt mad."
Why mad? we asked.
"Because, what her actions did, and what he did."
He is 45-year-old Kevin Esterly. The family says they met Esterly years ago at church.
Amy quickly became friends with one of his four children. They spent time at each other's houses.
In fact, Mul Luu even had Kevin Esterly over to their home for dinner.
"Yeah, just a plain nice guy, that tries to help Amy," John says of his early impression of Esterly.
Then he adds, "But not anymore."
Not after her mother discovered text messages on Amy's phone…hundreds of them. She told us Amy was talking to Esterly as if he were her boyfriend.
"Now I think he's a very bad guy and Amy's not hanging out with the right person," John says.
After more digging, Mul Luu says she was shocked to find out Amy had been signed out of her school, Lehigh Valley Academy Regional Charter School, 10 times by Esterly.
The school released a statement saying in part: "Whenever a person comes to the school and requests to remove a student they are asked to present identification, and, if the identification matches a person on the emergency contact list, the student is released to that individual. We can't comment on student matters or this specific case but we hope that Amy comes home safely and soon."
Amy's mother claims she didn't put Kevin Esterly on any emergency contact list.
"We never knew," says John.
The family says they believe Esterly had a plan to convince Amy to run off with him all along and on Monday, they think he finally did.
"I pray to God and God help me to bring her back," Amy's mother says, putting her hands together in prayer and looking up.
They say Esterly took advantage of a young girl and they are begging Amy to come home.
"Please come back," John says. "We need her to come back."
Police have an arrest warrant out for Kevin Esterly charging him with interference with custody of children.
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