Tuesday marks 17 days since the 61-year-old has been seen in public, and despite a clamour of rumours of ill-health, the Tanzanian authorities have yet to provide clear answers as to his whereabouts.
The mere question is now leading to arrests, as the government seeks to contain the rumours.
And analysts say the silence is telling.
"I think whatever happens ... it is clearly true the regime is trying to buy time," said Nic Cheeseman, professor of democracy at the University of Birmingham.
"And it only really makes sense that the regime is trying to buy time if the president is very ill, incapacitated, or dead."
Magufuli last appeared in public on February 27, and the fervent Catholic has missed three Sunday services, where he would often address the congregation.
Just days before, Finance Minister Philip Mpango appeared coughing and gasping at a press conference outside a hospital, to dispel rumours he had died of Covid-19.
Tell the truth
On Monday, Lissu said on Twitter that his intelligence sources "say he's on life support with COVID and paralysed on one side and from the waist down after a stroke. Tell the people the truth!"
Among the theories in circulation is that Magufuli is severely ill in a hospital in Kenya or India, while another suggests he never left Tanzania at all.
Kenyan media have reported the presence of "an African leader" in a Nairobi hospital in clear reference to Magufuli, although government officials deny he is present.
India's foreign ministry did not respond to requests for comment.
Cheeseman said it was "remarkable" that the government has kept Magufuli's whereabouts under wraps "in the modern world of the internet and citizen reporting and social media".
"But Tanzania isn't living in that modern world. The... level of media censorship means Tanzania is not in that context."
The Tanzanian government has said very little, other than to threaten those spreading rumours with jail time.
Unnecessary secrecy
Meanwhile Tanzanians say they want to see their leader in person.
"I believe something is happening but the authorities are hiding," said Muhsin, a resident of the financial capital Dar es Salaam.
"I will be comfortable if I see the president himself."
Clothes vendor Deborah said there was "unnecessary secrecy".
"If our beloved president is really ill, they should tell us the truth so that we put him in our prayers," she said.
Magufuli came to power in 2015 as a no-nonsense, corruption-busting president nicknamed the "Bulldozer", and was re-elected in a disputed poll last year.
However he has been accused by rights groups and of stifling democracy, and cracking down on the media.
As a result, the country's journalists are too afraid to dig into the story.
"It's all about survival and telling the truth... you need to play it safe to continue operating or rush to this delicate story and risk your licence and most importantly your life," an editor of a privately-owned Swahili newspaper said on condition of anonymity.
The government has also started cracking down on people whom it accuses of spreading the "rumours" that Magufuli was ill through social media, threatening to charge them with cybercrime offences.
So far police have announced the arrest of one person in Dar es Salaam and two in the northern Kilimanjaro region for spreading rumours.
"Rather than give credible evidence that he's alive and well, they're arresting innocent people who want to know the truth," said Lissu.