Mom of missing girl, 16, who may have fled to Cancun with older man pleads: 'Can you come home?'

The mother of a missing 16-year-old Pennsylvania girl who is believed to have run away with a 45-year-old man sent a message to her daughter in an interview with ABC News.

"Amy, I love you, can you come back?" Miu Luu of Allentown, Pennsylvania, said Friday, addressing her daughter, Amy Yu.

Yu along with Kevin Esterly, 45, have been missing since March 5, and police believe the teen left with the man willingly.

When the girl did not return home from school that night, her mother reported her missing, the Allentown Police Department said.

Two days later, police received information indicating that on the night of March 5, Yu and Esterly took a one-way flight from Philadelphia to Cancun, police said.

Luu reported to police after her daughter's disappearance that money, jewelry and Yu's personal documents were also missing, according to a police report.

The mother told ABC News she doesn't care if her daughter has spent her money, she just wants her to come home to her and her brother.

The girl's brother, 15-year-old John, added, "I hope you come home safely. Please don't get into any trouble, and just get home safely."

An Amber Alert has been issued in Mexico for Amy Yu.

"Prior to the Amber Alert in Mexico, the information that Amy Yu and Kevin Esterly were likely in Mexico was not released as it is believed that Kevin Esterly and/or Amy Yu are monitoring media reports," police said in a news release Friday.

John Waldron, the attorney for Esterly's wife Stacey Esterly, confirmed to ABC News that over several years Yu became a "fifth daughter" to their family.

That changed over the last "eight or nine months" when Waldron said Stacey Esterly learned the patriarchal relationship became "sexual."

"She tried to prevent Kevin on almost a daily basis from having contact with Amy," Waldron said, adding that Stacey Esterly didn't report him to authorities at first because she was concerned about fracturing her family.

But after a harassment charge was brought by local authorities against both Kevin and Stacey Esterly in what Waldron described as being "over a cell phone and text messages," Stacey Esterly was ready to open up about the questionable romance and her overtures likely sent her husband to take flight.

"It was reaching a breaking point which is part of the reason why Kevin ultimately took off with Amy," he said. "Because he knew that Stacey was going to take more drastic measures with the authorities."

Allentown police issued a message to the teen Friday, "Amy, if you are uncertain how to come home or who to contact for help, you may simply reach out to a law enforcement official, a resort staff member, or contact your mom via text message, email or social media, and we will work to reunite you with your family right away."

Esterly met the teen at church, and Amy Yu appears to have been friends with one of Esterly's daughters, said Gary Hammer of the Colonial Regional Police, which has jurisdiction over her school, Lehigh Valley Academy.

When Amy Yu was asked by members of the Leigh Country Child Advocacy Center whether she was having a relationship with Esterly, she denied it, Hammer said.

However, Amy Yu altered her school records and listed Esterly as her stepfather, Hammer added. And at least 10 times between December and Feb. 9, Esterly signed her out of school early, he said.

Feb. 9 was the day when Luu 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.

"The mom explained she is a single mother," Hammer said. "There is no stepfather."

Lehigh Valley Academy confirmed that Esterly has been on school grounds before and was last there on Feb. 9.

"After that date, due to circumstances we cannot disclose pursuant to student privacy constraints, he was prohibited from entering school grounds, and the police were to be notified if he returned," the school said in a statement last week.

The school said in its statement, "Due to federal and state privacy constraints, the school is prohibited from releasing any additional information about the student or the facts and circumstances surrounding the situation unless the parent provides express consent for the school to do so.

"We are, however, working closely with the Colonial Regional Police and the Allentown Police and are providing whatever information and assistance we can to assist them and Amy’s family during this difficult time," the school added.

The school called the Colonial Regional Police immediately and it started investigating. The department found video of Esterly signing the teen out and leaving with her, Hammer said.

On March 7, a family member of Esterly reported him as missing or endangered, and that same day, an arrest warrant for Esterly was issued, charging him with interference with the custody of children, the police said.

Amy Yu is about 4 feet 11 inches tall and 90 pounds, and Esterly is 5 feet 9 inches tall and 185 pounds, according to police.

Anyone who sees either of them is asked to call 911, local police or the Allentown Police at 610-437-7751.

ABC News' Matt Stone, Tom Kelly and M.L. Nestel contributed to this report.