Independent watchdog Freedom House looked at how online discourse was influenced by governments, bots and paid opinion formers.
In total, 30 governments were actively engaged in using social media to stifle dissent, said the report.
Educating users to spot fake news and making tech firms police their networks could combat the manipulation, it said.
Devastating impact
The annual report studied the state of internet freedom across 65 nations - covering about 87% of the world's net-using population.
