I am sure what the stalker is doing is illegal under Australian laaw as well as U.S. law. Unfortunately, the international situation makes this somewhat hard to deal with.
Your local police might be willing to contact his local police to make a personal visit to tell them to cut it out. They Austrailian police may even be willing to go further as this is a minor they are dealing with.
You could hire a lawyer to write a cease and desist letter to the stalker - it has lillte legal force, but could threaten serious criminal & civil sanctions.
Finally, I know the youth of today do not know their electronics have an off button, but my suggestion is to turn skype off until the stalker finds another fish to fry.
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Call both the FBI, the police in Australia, and the folks at Microsoft, which owns Skype.
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