A 21-year-old woman from Vlakfontein, south of Johannesburg, alleged to have been kidnapped had not yet been found on Monday, police said.

The woman was reportedly taken hostage on Friday, said Warrant Officer Kay Makhubela.

"She left her home in the morning and said she was going to go look for a job," Makhubela said.

"At around 5.45, the woman's grandmother received a WhatsApp message saying she must bring R30,000 cash within 24 hours or she won't see her granddaughter again."

The message also contained information on where the money should be dropped off.

The grandmother reported the incident to the Lenasia police.

"As the police, we also traced the place from where they were contacting her from," said Makhubela.

The kidnappers were no longer at that location and they did not arrive at the organised drop-off point.

She had not yet been found on Monday morning, said Makhubela.

Police were investigating a case of kidnapping.