A 16-year-old girl has gone missing from Sydney's south just 24 hours after she arrived back in Australia.

Cassie Olczak, from Sylvania, was last seen on Sunday when she boarded a southbound train at Banksia railway station just before 7pm.

Missing: Sydney teenager Cassie Olczak. Credit:NSW Police

She was expected to alight from the train at Hurstville but police and her family said they did not know if she ever arrived there.

The teenager had arrived back from visiting her father in Abu Dhabi on Saturday night.