Speaking at a protest on Wednesday outside the Saudi embassy in London, Almasarir said Khashoggi's slaying had shown the wider world a darker side to the power wielded by Prince Mohammed.
"If they are not held accountable, they will continue to do it," the 38-year-old said, adding that many Saudi dissidents living in Britain were "afraid right now to leave their houses".
Riyadh faces growing incredulity over its explanations about the killing of Khashoggi, a Washington Post contributor and critic of Saudi policies.
After he disappeared at the Saudi consulate in Istanbul on Oct. 2, Saudi officials said he left unharmed. But on Friday they announced he had been killed inside in an altercation.
World powers including Britain and France are demanding answers and US President Donald Trump has accused Saudi Arabia of lying about the murder.
Almasarir and a dozen activists hired an old-fashioned, open-top red London bus to drive past the Saudi embassy for their demonstration, chanting "Where is the body of Jamal?" and accusing Prince Mohammed of being behind his murder.
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The bus was plastered in banners reading "Justice for Jamal", which the demonstrators then unfurled outside the security fence surrounding the plush 18th-century mansion in central London.
From self-imposed exile in Britain, the video-blogging political satirist, who regularly roasts the ruling Saudi royal family, has racked up more than 200 million views on YouTube.
His outspoken anti-regime criticism has also earned him enemies.
On August 31, just over a month before Khashoggi was killed, Almasarir said he was followed and beaten by two Saudi men.
The scene — in which he was punched in broad daylight opposite London's Harrods emporium landmark —was captured on video.
Khashoggi's death has caused such a wave of fear among exiles that some are now cautious of even visiting their country's overseas missions.
Looking at the wrought iron gates of the Saudi embassy, Almasarir said he has no plans to step beyond them any time soon.
"If we happen to walk inside, I think we will end up like what Jamal Khashoggi has suffered.
"They might kill us and dismember our bodies," said the dissident, who has political asylum in Britain and said he has refused invitations to renew his Saudi passport at the embassy.
After emerging as first-in-line to the Saudi throne in June 2017, Prince Mohammed gained popularity after shaking up the ultraconservative kingdom with fundamental reforms.
However, his image has been tarnished by Khashoggi's killing and many critics now see the 33-year-old's crackdown on dissent as verging on authoritarianism.
Saudi Foreign Minister Adel al-Jubeir has blamed the murder on a "rogue operation" by individuals who "exceeded their responsibilities" and then "tried to cover up for it".
But Western governments have said many questions remain unanswered and that the Saudi explanations so far lack credibility.
"A lot of people around the world have the wrong image of the Saudis," said Almasarir.
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If critics were being murdered abroad, it begs the question as to the fate of domestic dissidents, he said.
"But I don't think we should be intimidated because we have freedom of speech," he added.
Almasarir's videos ridicule in particular the crown prince — the power behind King Salman's throne.
"I mock the Saudis. I nickname the crown prince Tubby Teddy Bear. I criticise them and make a joke out of them and their decisions," he said.
Almasarir said international pressure over Khashoggi's murder should lead to Prince Mohammed being prosecuted.
"If they refuse to do so, the international community should get together and impose sanctions on him personally. He should be banned from travelling," the social media star said.
Some American politicians are calling for tough action if a link to the Saudi royal family is proven. Saudi officials say the crown prince did not order the killing.
Still, Britain and the US have already imposed visa bans on the people identified as potential suspects in the murder.
Almasarir said he hoped the global outrage would bring change to the kingdom, pointing out that 94 per cent of his YouTube hits come from within Saudi Arabia.
"The Saudi people are fed up with the government, they don't trust them and they see my show as a voice for them."
He said people watched his YouTube channel "in secrecy but I hope that one day (they) will share it and it's not a crime in Saudi Arabia."
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