Missing Aussie woman Sara Zelenak was last seen on London Bridge before the terror attacks

Family and friends of this Australian woman have launched a social media campaign to desperately try and find her after she was last seen on the London Bridge.

Sara Zelenak, 21, from Brisbane, was last seen on the bridge before the terror attacks on Saturday night.

She has not answered her phone since, despite calls and texts.

A Facebook post written by a family friend titled "Missing from London Terror Attack" has been shared more than 500 times.

This post read: "Dear friends please can I ask you to share this post. My friend's daughter, Sara Zelenak, was last seen on London Bridge and was witness to the terror attacks," the post reads.

"She got separated from her friends and has not been seen since. Her phone has rang with no reply and now the battery must have gone.

"She is Australian aged 21 with long blonde hair. She calls her mum daily. It's been over 24 hours with no news from the consulate. We was hoping the 3rd Australian reported would be her, but it's not.

"She is based in London. Please share with as many people as possible especially if you have friends down south. Thank you for your help."

The Facebook post has since been removed.

Sara Zelenak. Photo/Sara Zelenak/Facebook

Another post has also been circulating on Facebook, saying: "Hi Everyone, This is my beautiful Australian friend Sara. She went missing after witnessing the attack on Saturday night, last seen on London Bridge. She got separated from her friend and we believe she dropped her phone in the chaos and now it is flat. No one has heard from her in over 24 hours now. The authorities have already been notified. If anyone has seen her or knows of her whereabouts please let me know. I know she did have quite a few Aussie friends in London so maybe you guys know something more. Please ask around and share this post with your friends.
We all want to make sure she is safe and need to get her home to her family
Thanks for your help xx".

Prime Minister Malcolm Turnbull confirmed today that four Australians were caught up in the attack. Two have been identified. Candice Hedge from Brisbane, and Andrew Morrison from Darwin. Both were hospitalised after the attack.