His conviction on charges that could have seen him jailed for up to three years has focussed attention on freedom of speech in Singapore's booming social media.

"I don't know if I should celebrate my release or mourn my sentence," 16-year-old Yee said after walking from a remand prison where he has spent 18 days.

Five days after the death in March of Singapore's founder Yee posted a blog on YouTube entitled "Lee Kuan Yew is Finally Dead!"

He shared it with a provocative online site The Real Singapore, one of several alternatives to Singapore's government controlled television and newspapers.

A day after he put up the video Yee uploaded an image illustrating two people having sex on which he superimposed the faces of Mr Lee and former British prime minister Margaret Thatcher.

Yee was arrested, charged and refused bail after the original post went viral locally, with more than one million views.

Open criticism is rarely tolerated in Singapore where the media has been tightly controlled for decades.

But as Singaporeans prepare to celebrate 50 years of independence in August, many are increasingly using social media to openly debate politics and social issues, creating a dilemma for the government.

Floppy-haired Yee, a high school drop-out who has criticised his teachers and parents, pleaded not guilty to two criminal charges during a two-day trial last week.

On Tuesday after he was found guilty, prosecutors said they were not calling for a jail sentence and requested a probation report to assess his suitability for probation and reformative training.

"His actions show him to be a misguided young man who sought to gain attention for himself by deliberately posting obscene material he admits he knew would cause ill among Christians," said deputy prosecutor Hay Hung Chun.

Defence lawyer Alfred Dodwell told the court that Yee did not want probation and asked to be allowed to walk free after the 18 days he had already spent in jail while under remand were taken into account.

Phil Robertson, deputy director in Asia for Human Rights Watch, said Singapore's actions to criminalise Yee's statements run contrary to international human rights standards and are a dangerous affront to freedom of expression.

"Singapore has one again proved that those who speak their minds in the city state do so at their own risk," he said.

"No wonder the youth of Singapore are increasingly worried about their future – since their government seems doggedly determined to gag their words on social media and shut down news portals putting out stories that don't agree with the government's political line."

Yee will be sentenced on June 2.