Wearing blue and yellow ribbons -- the colours of both Ukraine and the European Union -- the crowd received a religious blessing before opposition leaders took to a podium on Independence Square in a bid to ratchet up pressure on Yanukovych to appoint a new pro-Western government.
"None of the kidnappings and tortures have yielded any results," said Igor Lutsenko, who was grabbed by assailants during deadly unrest in January and beaten up at the same time as another activist who was later found dead.
Speaking from Lithuania where he is being treated after being tortured, Dmytro Bulatov, another activist, said he had no intention of giving up.
"We will go further," he said by phone in a conversation broadcast over a loudspeaker to the crowds.
The ex-Soviet nation of 46 million people has been thrown into chaos since November when Yanukovych ditched an historic EU trade and political pact in favour of closer ties Moscow, stunning pro-EU parts of the population and sparking violent protests.
Since then, what started out as a localised, domestic bout of unrest has snowballed into a titanic tussle for Ukraine's future between Russia and the West, as demonstrations continue and spread to other parts of the country.
'Like Somali pirates'
Yanukovych has already yielded to some opposition demands by dismissing the government, but he also has to appease Russia, which has effectively frozen a much-needed $15 billion (11 billion euro) bailout until the situation clears up.
The embattled Ukrainian leader held talks with Russian President Vladimir Putin on Friday in the Black Sea resort of Sochi on the sidelines of the opening of the Winter Olympics.
It is unclear what the two discussed, but Yanukovych had been expected to raise the issue of the bailout, of which Russia has so far issued only one instalment of $3.0 billion.
"We hope that authorities will make concessions and that agreements with the opposition will bring results. Because the authorities look like Somali pirates who take hostages and then negotiate," 29-year-old Oleksandr Zaveroukha, who had come from western Ukraine, told AFP in Independence Square.
"We are determined to stay until the end."
On the square, the crowds listened attentively to the speeches from the podium, out in force on a relatively mild day for the Ukrainian winter.
The size of the crowds roughly equalled the turnout last weekend, but was markedly lower than at the end of January, when protests degenerated into violence that left several people dead.
'Protesters a key wildcard'
Alex Brideau, an analyst for political risk consultancy Eurasia Group, said the actions of the protesters were a "key wildcard in the political standoff", noting that their "continued frustration with the lack of progress on their demands" was a major factor behind the violence at the end of January.
Leading Ukrainian lawmakers are expected to meet on Monday to discuss opposition proposals to slash presidential powers and return to a pre-2010 constitution that swayed the balance towards parliament.
Yanukovych has signalled that he welcomes a discussion of the changes without committing himself to the reform.
But Ukraine's tattered economy is in ever-growing need of assistance amid sliding domestic production and dwindling foreign reserves.
Moscow is already demanding the repayment of a $3.3 billion debt that Ukraine built up since last year for Russian natural gas imports on which the country's industries and households depend.
Putin's bailout would slash the future price of Russian gas imports by a third -- a huge relief for the economy that analysts believe should help revive stalled growth.
But Russian Economy Minister Anton Siluanov warned on Saturday that Moscow would need at least a partial down payment on the outstanding gas bill before the terms of its Ukrainian package are restored.
The protracted crisis has seen Ukraine's borrowing costs spike and the currency lose nearly 10 percent of its value as frightened consumers rush to stock up on dollars and euros.
Several banks have reported hard currency shortages and the central bank on Friday was forced to impose capital controls and move the Ukrainian hryvnia's official rate to 8.7 from 7.9 per dollar -- its first shift of the peg since July 2012.