Woman missing in Sydney for four days

Relatives of a young NSW woman who hasn't been seen for four days are increasingly concerned after she failed to return home for her birthday.

Tasnubah Mahmud was last seen going for a walk from her family's home in Minto, in Sydney's southwest, on Sunday afternoon. She turned 26 on Thursday.

Ms Mahmud didn't take her phone or wallet and is not believed to have any money with her.

Chief Inspector Mark Brett says the family is worried because she relies on daily medication to help with a condition.

"The important thing here is if someone sees her, maybe she's a bit disorientated because of the lack of medication," he told AAP.

"If someone sees her, just approach her and ask her is she OK and try to elicit her name."

Police have released CCTV footage and Ms Mahmud's photograph.

Her family had checked with a "limited number of friends" but none had heard from her, Insp Brett said.