There are a number of online tools and directories for finding people in Australia, including Reverse Australia and Person Lookup. Another potentially useful tool is Facebook, but much will depend on how much information one has on the person to begin with.
For instance, if a person's phone number is known (whether their home phone number or cell), Reverse Australia (reverseaustralia.com) can be used to track down their general registered whereabouts. Users need only enter the Australian telephone number and area code, then log in with Facebook. Results typically list a person's name, a map of the rough area of their home address and the age of the information.
Person Lookup (personlookup.com/au) is similar, but allows users to input either a surname, a partial (or complete) address or a partial (or complete) contact number. Results then list all the names, addresses and phone numbers that are a match for the provided information.
Although there may be some concerns about privacy, the information held by Person Lookup is all in the public domain already. Those wishing to have their information removed from the database may contact the company.
Using Facebook to find someone in Australia is another option. Users can enter the name or email address of the person they are seeking, then send an invitation to be friends with them. At this point users will have access to whatever information their new friend has made accessible to them.