The younger of the two girls has been missing for four days and did not turn up to school on Monday.

Lasela Fue, 12, was last seen at her home in the town of Traralgon in Victoria's east on Thursday, October 1.

"It is believed that she may still be in the Latrobe Valley area, however she is known to frequent the Melbourne CBD," a police spokeswoman said.

"Police have concerns for her welfare, because she has not returned home."

Lasela is Caucasian, with black hair and brown eyes.

Police also hold concerns for missing 14-year-old girl Jade Robson-Whitehouse, who was last seen at her Junction Village home in Melbourne's south-east on Saturday, October 3.

Jade's anxious family told police that the teenager disappeared with a female friend she met online using a fake Facebook account, after she invited the friend to stay over.

The pair reportedly fled the house after Jade's step-mother, Tracey, tried to make contact with the friend's parents to let them know where she was.

While Jade has been in touch with at least one friend on Facebook, her parents and police remain concerned for her welfare.

Jade did not attend school on Monday morning

"It's just horrible to not know where your child is," stepmother Tracey said.

"I can't sleep, I can't eat. I just want her to be home, I can't explain it."

Jade is described as being about 150 centimetres tall, with a slim build, long auburn-coloured hair and green and brown eyes.

She does not have any money or a mobile phone in her possession.

Anyone with information about Jade's whereabouts is urged to immediately call triple-0, Narre Warren police station on 9705 3111, or Cranbourne police station on 5991 0600.

Anyone with information about Lasela's whereabouts is urged to call triple-0 immediately, or contact Traralgon police on 5172 2700.