Facebook has refused a police request to take down a page with prejudicial comments about the man accused of murdering Melbourne woman Jill Meagher.

There was a huge response to the disappearance of the 29-year-old ABC employee on social media, with a Facebook page set up to find her attracting more than 120,000 likes.

Police say the social media campaign to find Ms Meagher helped their investigation, but they are now concerned about the potential for trial by social media.

Adrian Ernest Bayley, 41, of Coburg, has been charged with raping and murdering Ms Meagher and will return to court in January.

Victoria Police Chief Commissioner Ken Lay has told Fairfax Radio that Facebook will not cooperate in removing the page and he is seeking legal advice.

"Though social media's been enormously helpful in this investigation, it's also been very, very difficult and we had cause to speak to Facebook over the weekend and ask them to take a particular site down," he said.

"Now, they've refused to do that.

"We've all got a social responsibility. Facebook is part of our community and I would have thought that it would have only been reasonable.

"When you see the hatred that's incited by some of these sites, it is very much the antithesis of what we saw yesterday with 30,000 people taking to the streets saying let's try and make this a safer and fairer community."

Facebook has not responded to a request for comment.

Police and Ms Meagher's husband Tom have urged people to be cautious about what they post online.

Mr Lay says some comments could jeopardise the case.

"We've got to remember that no matter how horrible this crime is, this gentleman has got to be afforded a fair trial.

"It's not for Facebook pages or anyone else to be taking justice into their own hands."

Premier Ted Baillieu has told ABC local radio that he is not sure if social media commentary undermines the jury system.

"In many ways social media is a recording of conversations that occur and perhaps traditionally occurred in pubs and clubs, in social venues.

"It has moved from undefinable gossip into almost resourced gossip, and it does have an impact."

Mr Baillieu says he has discussed asking the Victorian Law Reform Commission to review whether legislative change is needed.

About 30,000 people marched down Sydney Road in Brunswick yesterday in memory of Ms Meagher.