The singer-songwriter wrote on Twitter that the investigation was a "sham" in a series of messages about the media and political system.
"It's interesting don't you think, that not one newspaper went near the things I said in defence of gay teenagers last week," Michael said.
"Those gay loving people at the Daily Mail should be admired for their consistent attitude to me. Not a word about those poor kids....
"But I gave them another chance to have a dig at me just by joking a little about my past. They really are pathetic, pitiful human beings...
He continued: "[Rupert Murdoch] has been called 'unfit' to run a major media company by MP's. Understatement of the year? (sic)
"And it's so funny that the Conservatives in government are defending him! Trying to cover their arses when those lily white buttocks... of theirs are already on display for the whole world to see. Cameron must be the most cowardly PM we've seen for decades."
Michael added: "One last thing... I was asked to talk to the Leveson inquiry, but I declined. It's all bulls**t.
"It has been several years since two hacking journalists were sent to prison for bugging the royal family. They remain the only people... who have been tried in the criminal courts. After all these years, and all the crimes comitted by journos,editors, the police force and MPs.
"The best can do is 'enquiry' after inquiry, and no actual criminal prosecutions? Why on earth are the rights of the royal family... more important than those of Milly Dowler's parents, or of any of the hundreds of people whose lives have been violated by the press?
"Shame on our political system for it's refusal to take this further. The day they make this sham real and start genuinely prosecuting people I would more than happy to help. :)....till then, what's the point."
Michael also claimed that the Daily Mail was "every bit as guilty of hacking and lying as Murdoch's bunch", though the newspaper has strongly denied such allegations throughout the course of the inquiry.
Ex-News International chief executive Rebekah Brooks and David Cameron's former communications chief Andy Coulson will appear at the Leveson Inquiry this week.