Demonstrations against the killing were seen in cities across the continent with left-wing radicals and other sympathisers taking to the streets.
In Spain, 11 protesters were arrested and several police officers injured when clashes took place in Madrid and Barcelona.
In Copenhagen, 32 people were arrested when their protest in support of the Greek protests turned violent.
In neighbouring Turkey, about a dozen left-wing protesters daubed red paint over the front of the Greek consulate in Istanbul.
Around 150 people belonging to a Danish underground movement took to the streets, throwing bottles and paint bombs at buildings, police cars and officers. In Moscow and Rome, protesters threw petrol bombs at Greece's embassies.
Journalists came under attack for the first time in the riots, with a Russian news crew assaulted by a mob of about 50 youths, some of them reportedly drunk.
A correspondent and a cameraman for Russian television channel NTV were injured in the confrontation, which happened while they filmed clashes in Exarchia, a crucible of student radicalism.
In Athens, around 40 youths threw stones at riot police near university buildings in the volatile Exarchia district where 15-year-old Alexis Grigoropoulos was shot dead on Saturday.
Greek protests spread with arrests across Europe