Speaking at the GLOBSEC security conference in the Slovak capital Bratislava, Cameron said Europe should focus on the Internet, used by the Islamic State "as the main tool to spread its warped worldview."
On July 1, the European Union's law enforcement agency, Europol, is due to launch its Internet Referral Unit to tackle the issue.
The Unit will "coordinate and share the identification tasks (flagging) of terrorist and violent extremist online content with relevant partners" and carry out referrals and analyses on the subject, according to its programme released by the EU in March.
In Britain "we are working with the Internet industry to tackle terrorist propaganda -- removing over 90,000 pieces of material since 2010," Cameron said Friday.
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Speaking to AFP earlier this week, EU counter-terror chief Gilles de Kerchove said an estimated 4,000 Europeans have so far joined the jihad in Syria.
De Kerchove also urged more thorough checks of those leaving the Schengen visa free area while admitting a lot remained to be done regarding the Internet.
"We've always had angry young men and women buying into supposedly revolutionary causes," Cameron told a dozen European leaders attending GLOBSEC.
"This one is evil."
Cameron said those young recruits left "often loving, well-to-do homes, good schools and bright prospects... To strap explosives to their chests and blow themselves up and kill innocent people."
Britain was recently shaken by the case of 17-year-old Talha Asmal, a Briton identified as the driver of one of four explosive-laden vehicles used in an attack on an oil refinery in northern Iraq a week ago.