The French president was reacting to an Islamic State video of beheadings of US hostage Peter Kassig and 18 Syrian servicemen.
The rally in the hometown of the hostage beheaded by Algerian Islamists, came as flags were lowered to halfmast across France in mourning.
France has authenticated a video of the beheading of Hervé Gourdel, which President Hollande said was a 'cruel and cowardly' act.
An Algerian Islamist group captured the 55 year-old tourist on Sunday and threatened to execute him unless France halted strikes against IS.
The French Prime Minister said French action against IS will go on despite Algerian Islamist group's threat to kill a French hostage.
Journalist Nicolas Henin said Mehdi Nemmouche, who has been extradited to Belgium over murders, was his jailer in Syria in late 2013.
Report claims that, despite denials, French authorities and other European nations pay out millions over kidnaps that then help finance terrorism.
Serge Lazarevic, who was captured two years ago by Al Qaeda's North African wing AQIM, called for help from President Hollande.
No details of why or when Gilberto Rodrigues Leal, 62, died were given by the al-Qaeda affiliated group who kidnapped him in 2012.
Nicolas Hénin says release of him and three other French journalists was a 'real surprise' and that he is 'filled with joy' but exhausted.
Francis Collomp, 63, who was kidnapped on December 19, 2012, by the Ansaru Islamist group, reportedly escaped during a shoot-out.
Didier François, a radio reporter, and photographer Edouard Elias were kidnapped near the northern Syrian city of Aleppo in June.
In a video released by his captors, Francis Collomp, kidnapped last December, asked for French and Nigerian help in securing his release.
Pierre Borghi, held captive for 131 days, escaped after losing 12 kilograms, allowing him to slip out of his chains and climb through a narrow window.