Mr Hollande, making his third visit to the UK, joined David Cameron in pledging to get to the bottom of the tragedy.
Speaking through an interpreter, he said: "I expressed my emotion earlier today to the British people in relation to the terrible deaths.
"We will do our utmost to find the perpetrators, to find the reasons."
Investigations are continuing after three members of a British family were gunned down in their car in the French Alps.
Saad al-Hilli, 50, who was originally from Iraq, was shot in the head alongside his dentist wife, named by neighbours as Iqbal, and a woman believed to be her mother.
The couple's four-year-old daughter, named as Zeena, was found alive in the BMW estate underneath the bodies of her relatives around eight hours after the massacre, which also saw a passing French cyclist, Sylvain Mollier, 45, shot dead.
The al-Hillis' seven-year-old daughter, believed to be called Zainab, was in a medically induced coma in Grenoble University Hospital after being repeatedly beaten around the head and shot in the shoulder in the attack.
Three of the four who were killed were shot in the head but investigators played down hints of "professionalism" .
Public prosecutor Eric Maillaud said: "I won't say it was professional, what I will say is it was tremendous savagery."
One of the family's neighbours in Claygate in Surrey said he was going to alert police to something Mr al-Hilli said to him before travelling to the Le Solitaire du Lac campsite close to the Swiss border.
Jack Saltman said: "I know one little thing which I am not prepared to speak about at the moment. I will tell the police about it."
The powerful BMW was discovered surrounded by spent bullet cartridges in a car park near footpaths on the outskirts of a forest near Lake Annecy, a popular tourist spot.
A British cyclist who had been overtaken by the French rider, discovered the grisly scene.
Police said the motive for the attack remained a mystery.
It was revealed that Swedish and Iraqi passports had been recovered along with the driver's British one.