The manhunt took place as friends and family tearfully mourned those slain - a rabbi, his two young sons and a young girl.
Authorities suspect the same killer was behind two recent attacks on French paratroopers of North African and French Caribbean origin that left three dead and one seriously wounded.
A "monster" is on the loose in France, French President Nicolas Sarkozy said, vowing to track him down.
France was reeling Tuesday after Monday's shooting in the southern city of Toulouse, the deadliest school shooting in the country and the bloodiest attack on Jewish targets in decades. Schools across the country held a moment of silence Tuesday to honor the victims, who were heading to Israel for burial after a wrenching farewell ceremony in Toulouse.
Interior Minister Claude Gueant said one angle in the case is that of three paratroopers who were kicked out of a regiment near Toulouse in 2008 for suspected neo-Nazi activity. He insisted it was just one of many motives being investigated and "not favored any more than the others."
Gueant said the attacker was "wearing around his neck an apparatus" that could be used to film and post video online. He said that gave investigators new clues to the killer's "profile," although he admitted they don't appear to close to an arrest.
Gueant described the suspect as "someone very cold, very determined, very much a master of his movements, and by consequence, very cruel."
In Monday's shooting, the attacker first gunned down a rabbi and his two young sons, then chased down the daughter of the school principal, shooting her dead at point-blank range. Reports of the children's ages varied, with the Israeli Embassy now saying the boys were 3 and 5 and the girl was 8.
Wails and weeping filled the air Tuesday as the school held a ceremony to honor the victims, including the rabbi who taught at the school. Several young men pressed their heads against the rear window of one of the hearses as it drove away.
The rabbi's widow covered her face and held her remaining child, a 1-year-old daughter, dressed in a bright pink dress.
The widow's uncle, Marc Alloul, described how the girl woke up in the middle of the night after the killings, calling out, "Papa! Papa!"
Sarkozy, who has played up nationalist themes in his bid for a second term in upcoming elections, sought to stress the overall horror of the crime.
"The children are exactly like you," Sarkozy told junior high school students in Paris after joining them for the moment of silence. "That could have happened here."
"There are beings who have no respect for life. When you grab a little girl to put a bullet in her head, without leaving her any chance, you are a monster. An anti-Semitic monster, but first of all a monster," he said.
He was speaking at a public school across the street from a memorial to the French people who helped Jews during the Holocaust, when most of France was occupied by the Nazis.
Sarkozy also spoke of the paratroopers killed in two attacks in Toulouse and nearby Montauban. The killer in those attacks also came and went on a motorbike and shot from the same weapon as one used in Monday's school killing.
"Is it because they had come back from Afghanistan? Is it because they came from visible minorities? We don't know," Sarkozy asked about the paratroopers.
The French Defense Ministry has said the paratroopers didn't serve in Afghanistan, but one family says their son did. Other families have refused to comment on the topic.
Sarkozy also met Tuesday with members of France's Jewish and Muslim community. France has western Europe's largest population of both Jews - about half a million - and Muslims - about 5 million.
The terror threat level was raised to scarlet across a swath of southern France - the highest level since the four-point system was created in 2003.
In Toulouse, France's fourth city, the town center is usually bustling with activity, but the streets were emptier than normal Tuesday. In one main square, Place Wilson, a dozen police officers were on patrol, some guarding the subway entrance.
The shootings echoed across a nation that has been focused on an upcoming presidential race in which issues about religious minorities and race have gained prominence.
All of the dead were dual Israeli-French citizens.
Police bearing automatic weapons stood in front of Jewish schools in Paris on Tuesday.
"It's impossible not to imagine the worst, because it can happen to any child in France at some point," said Mendy Sarfati, a father dropping his three children off at a Jewish school in Paris. "We want to put this drama behind us and for the French Republic to draw lessons from it."