More needs to be done to stop small social media websites being exploited by extremists, experts have said.
The likes of Facebook and Twitter have responded to calls to remove extremist content over the last 18 months.
And some smaller social media sites have joined a scheme where information is shared to enable blocking content.
But a major conference in Swansea, featuring key figures involved in tackling violent extremism, heard too many small sites were being "swamped".
Adam Hadley, director of Tech Against Terrorism, an initiative launched by the United Nations' Counter-Terrorism Committee Executive Directorate (CTED), wants politicians around the world to work together.
"Despite what newspaper headlines may say, a lot of propaganda and terrorists content exists on small platforms that no-one has ever heard of," he said.
"Policy makers and politicians talk about the big problems of Facebook and Twitter but unfortunately the problems surrounding the smaller platforms are completely ignored.
"You can't turn off the internet and we don't want to do that.
"There's a whole eco-system of these very small sites that can be completely swamped."
Tech Against Terrorism works with the Global Internet Forum to Counter Terrorism (GIFCT) - founded by Facebook, Google, Twitter, and Microsoft in 2017.
But it focuses on helping smaller sites such as those which are file sharing such as Telegram, JustPaste and Live Leak, and apps such as wickr.
Speaking from the International Countering Violent Extremism Research Conference at Swansea University, Mr Hadley said: "The biggest challenge is the lack of strategy from governments. Blaming technology is easy.
"But terrorists are not stupid. They are very good at technology. A lot of groups host their own websites and a lot of terrorists have their own servers.
"Countries need to talk to one another but it hasn't happened. Let's step back and develop a coherent strategy - which requires political will."
GIFCT members created a shared industry database of "hashes" - a unique digital fingerprint which can be used to track digital activity.
When pro-terrorist content is removed by one of the member, its hash is shared with other participating companies (including small sites) to block the content on their own platforms.
It is on track to meet its target of 100,000 hashes by the end of 2018.
Prof Stuart Macdonald, from Swansea University's Cyber Threats Intelligence Centre, said: "It's difficult as there's so much propaganda and it's appearing so quickly.
"Smaller platforms provides a safe space to radical groups and they can express themselves more freely."
He added: "There's lots of research that seeks to understand more about the individuals that do engage more with extremist material."