A 15-year-old girl from Chatswood had to call off an "open house party" she had organized on Facebook, when more than 20,000 people claimed they would be attending.
The party was meant to be a quiet get-together with a few friends from school but the invitation went viral within 24 hours, reports the Daily Telegraph.
This led her to cancel her 16th birthday bash and subsequently remove the event from the social networking site.
However, a replica invitation appeared an hour later.
The hoax invitation has continued to attract interest, with 50,000 guests listed as attending at lunchtime today.
Police are now looking for the creator of the fake invitation.
Chatswood Inspector Peter Yeomans said parties advertised on Facebook were a bad idea.
"It has a huge number of hits online and has the potential to turn very serious," he said.