She was expected to alight from the train at Hurstville but police and her family said they do not know if she ever arrived there.
The teenager had arrived back from visiting her father in Abu Dhabi on Saturday night. Cassie was reported missing to police on Sunday night with her family saying her disappearance is completely out of character.
“She came off a plane 7pm Saturday night, she came home, she ate, went to bed, was eager to meet up with her friends the next day,” her mother, Connie Olczak, said.
“The next day her sister drove her to her best friend’s house, they said she was fine … as the day went on she was highly agitated and they told her to go home and get some sleep.
“They last saw her at 6:58pm at Banksia station heading south. No CCTV confirms her getting off a train.”
Cassie was last seen wearing a multi-coloured shirt, grey tights and white and gold adidas sneakers.
Mrs Olczak said there had been reports someone fitting Cassie’s description and wearing the same clothing sleeping on the 5:37am train from Blacktown to Emu Plains with a pink blanket.
She said she did not know why her daughter would be in that area. Cassie has not accessed her bank account and her phone has been switched off since 8pm on Sunday.
Mrs Olczak said she had contacted her daughter’s friends and no one had any idea where she would be.
“She’s a quiet kid, she won’t go where there’s a lot of people,” she said. “She’s not street smart.”
NSW Police on Tuesday said they had concerns for Cassie’s welfare because of her age.
“Police have conducted extensive inquiries to date to try to locate Cassie, but at this time have been unsuccessful,” a police statement said.
Cassie is described as being of Caucasian appearance, about 175cm tall with a thin build and dark brown hair.
Anyone who has seen Cassie, or is aware of her whereabouts, is urged to contact CrimeStoppers on 1800 333 000.