The attacks, using gas canisters, also targeted a local party office operated by Greece's ruling conservative party.
There were no victims, but firefighters were called out to extinguish blazes with neighbouring stores also suffering damage to property.
Two cars were also burnt out in the busy Guizi and Exarchia areas of Athens . A week of unrest was triggered in Exarchia with the fatal shooting of 15-year-old Alexis Grigoropoulos.
There were no organised rallies planned for the day, but youths occupying nearby university buildings have said they will gather over the weekend at the spot where the schoolboy died.
Peaceful tributes are to be paid to Grigoropoulos, although authorities remain on alert.
Riot police again clashed with youths on Friday, the seventh day of Athens street protests, as Greek Prime Minister Costas Karamanlis dismissed opposition calls to quit.
"At this time the country faces a serious financial crisis... a steady hand on the helm is needed to deal with it," Karamanlis said. "That is my concern, that is the priority of the government, not scenarios about elections and successions.
"The compassion with which all of us ought to treat the distress of young people cannot be confused with blind violence, with the activities of extreme elements."
The offices of lawyer Alexis Kougias, representing two policemen awaiting trial over Grigoropoulos' death, were trashed, while in Paris, demonstrators blocked traffic on the Champs-Elysees after security was beefed-up at the Greek embassy.
In Berlin 1,500 people, about 150 of them Greeks, joined a peaceful march late Friday protesting the boy's death, organisers said. Police put their number at 500.
In Greece hundreds of banks, stores and public buildings have been destroyed, badly damaged by fire or looted in a week of violence mainly involving youths. Statistics show one in four aged 15-24 are officially unemployed.
And while normal life has returned to most of Athens, with protests falling off across provincial Greece, prominent university sites -- beyond the reach of law enforcement -- remain occupied.
The officer who shot Grigoropoulos says he was defending himself from a gang of youths and killed the boy by accident due to a bullet ricochet. A ballistics report, said to confirm that the handgun was not pointed at him, has yet to be released.