Marking his 63rd birthday, Fillon was trying to turn the page on a nightmare week that saw scores of defections from his camp after he admitted he is to face criminal charges over allegations he gave his family fake parliamentary jobs.
With some members of his own rightwing Republicans party urging him to drop out of the campaign, Fillon told 1,500 supporters he had had "better" birthdays.
Without referring directly to his legal woes, he said at a campaign event north of Paris: "They are trying to intimidate you. They are attacking me. But... What they are trying to kill is a desire for change."
As he was giving his speech, his Republicans party announced that its political decision-making body would meet Monday evening -- a day earlier than planned -- "to evaluate the situation".
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It also emerged that police raided the Fillons' country manor house near the northwestern town of Le Mans yesterday, looking for evidence. The couple's Paris apartment was searched on Thursday.
Fillon will attempt to regain the initiative by holding a major rally tomorrow near the Eiffel Tower.
Opinion polls currently show that far-right leader Marine Le Pen and 39-year-old centrist Emmanuel Macron would progress to contest the runoff on May 7.
Fillon was the frontrunner until mid-January when the Canard Enchaine newspaper alleged he paid his British-born wife Penelope and two of their children nearly 900,000 euros (USD 950,000) as parliamentary assistants or advisors.
French lawmakers are allowed to employ family members, but investigators are searching for evidence of what work Fillon's wife did.
He revealed Wednesday he is to meet investigating magistrates to be charged on March 15, sparking a series of defections from his team.
The left-leaning Liberation newspaper wrote: "It is no longer the rats leaving a sinking ship, but the ship leaving the rat."
With just seven weeks to go before voting begins, the entourage of 71-year-old former premier Alain Juppe has said he is prepared to take over.
But high-profile Fillon supporters from the business world rallied round him.
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