A 16-year-old girl who has been missing with a 45-year-old man since Wednesday named him as her stepfather on paperwork at her school so that he could sign her out without her mother's knowledge.

Amy Yu has not been seen since March 5. Police say she is with Kevin Esterly who signed her out of school at least 10 times between November 13 and February 9 without her parents' permission or knowledge.

Amy is friends with his daughter and he and his wife have been over to her family's home before.

He had been told to stay away from the girl after it was discovered that he had signed her out of school 10 times between November 13 and February 9.

Amy Yu, 16, told staff at her school on Pennsylvania that Kevin Esterly, 45, was her stepfather so that he would be allowed to sign her out. He is the father of one of her friends and the pair, who are in a 'secretive' romantic relationship, have been missing since March 5

On February 15, another incident occurred at her home which prompted Amy's mother to call police.

When they arrived, they told Esterly and his wife Stacey to stay away from the girl.

Amy and Esterly were in a 'secretive relationship' which was laid bare in text messages between them which Amy's mother discovered on her phone.

It is not clear if she found them before or after they went missing together.

On March 5, the pair are believed to have left Allentown, Pennsylvania, in a 1999 Red Honda Accord.

Amy was last seen by her brother who said she fled after being dropped off with him by their mother at their school bus stop.

Before fleeing, Esterly withdrew $4,000 from his bank accounts, his wife Stacey told police.

Esterly had signed Amy out of Lehigh Valley Academy school in Allentown, Pennsylvania (pictured) 10 times between November and February 9

Esterly and his wife Stacey befriended Amy's family through the church they both attend. She is friends with one of his daughters, seen with him above

Stacey told police that her husband withdrew $4,000 in cash from their accounts before he vanished with Amy on March 5

Amy's mother Mul Luu has not seen her since she dropped her off for the school bus on March 5

Amy's mother discovered after her daughter vanished that she had taken some of jewelry, her passport and cash.

Amy's younger brother and mother say they met the Esterly family through church.

They had them over for dinner at least once and Amy's brother John said it seemed the man wanted to help his sister.

'We never knew. Now I think he's a very bad guy and Amy's not hanging out with the right person,' John told WFMZ.

Their mother speaks limited English. Her mother said she's praying for her child's return.

'We need her to come back,' John said.