Update 3 October 2012:
On Saturday 29 September 2012, 30,000 people took part in a Peace March along Melbourne's Sydney Road, Brunswick where Jill Meagher was last seen alive. After news of her death, numerous Facebook pages titled R.I.P. Jill Meagher had sprung up.
One page had over 300,000 likes and this one  captured the moving scene:
Two legal issues have arisen. Police were in protracted negotiations with Facebook over distasteful FB pages before they were finally taken down. There were also concerns that they might prejudice a fair trial .
On a broader front, States Attorneys General are to discuss the legal implications of social media and the law, with calls for restrictions . Madeleine Ross at B&T , an advertising, marketing, media and PR website, explored some of the issues:
Media lawyers have today come out to defend social media in the midst of a heated national debate about the swelling power of Facebook and Twitter.
…The death of ABC staffer Jill Meagher in Melbourne last week also sparked debate when Facebook refused to pull down pages which featured hateful and violent commentary directed at Meagher's alleged murderer.
…The confusion around what is and what should be illegal on social media seems to stem fundamentally from a disconnect in the way people perceive the medium; that is, should it be considered a forum for open public discussion, reflective of everyday face-to-face chatter, or should Facebook and Twitter pages be considered as publishing channels?
28 September 2012:
This week Melbourne has seen what is perhaps its biggest and its saddest social media campaign following the disappearance and alleged rape and murder of Jill Meagher. From Meagher family, friends pay tribute to Jill :
Friends, colleagues and the public have taken to social media to leave tributes to ABC employee Jill Meagher.
… Ms Meagher's husband Tom has thanked members of the public for their “humbling” support.
Jill was a staff member at the ABC Radio 774, part of the Australian Broadcasting Corporation. She and her husband Tom came to Australia from Ireland three years ago. After she went missing in the early hours of Saturday 22 September, a Facebook campaign Help us find Jill Meagher  attracted extraordinary attention with 122,253 likes and 133,998 talking about this by Friday 28.
Other Facebook pages such as Missing Jill Meagher  also sprang up. Some sought help with identifying CCTV video  released by police. Most of the visitors to these pages were trying to be helpful but there were the inevitable trolls on Facebook sites and twitter. They do not bear repeating here but ‘Can we please stop the victim blaming? ‘ documents some of the ways in which “self-fancying armchair detectives had already taken to social media to share their uninformed, moronic theories on what might have happened”.
BBC foreign correspondent Nick Bryant , who has worked in Australia for several years, tweeted sentiments shared by most Melburnians following news of her death:
@NickBryantOz : Have seldom heard such dignified and moving broadcasting - @774melbourne  remembers and celebrates one of its own. http://www.abc.net.au/melbourne/programs/listenlive.htm  28 Sep 12
The charging of the alleged killer has brought warnings about possible unintended negative consequences of social media comment. Matthew Knott of crikey.com reported :
The family and former colleagues of Jill Meagher have urged social media users not to publish prejudicial statements about the man charged with the rape and murder of the ABC employee because of fears they could impact on a future trial.
Professor Sarah Joseph  of Monash University’s Castan Centre for Human Rights Law help spread advice that was retweeted numerous times within hours of posting:
Please (wearing my lawyer's hat now) remember the following:
1. The presumption of innocence, regardless of how strong the Crown case appears to be.
2. The matter is now sub judice. Do not speculate on it.
3. If you see a Facebook page or online forum wishing death or dismemberment or prison rape on the accused, report it to Facebook or to the site owners.
4. Go back to number (1).
These warning were backed up by the Victoria Police  on Twitter:
Let’s hope that people take this advice.