The future King said much of the climate of optimism the internet had ushered in had given way to concern and fear.
The big technology firms, he said in a hard-hitting speech, “still have a great deal to learn” about their responsibilities”.
William acknowledged that the companies were run by “people of integrity”, but he challenged them to fight harder against poison spread online.
He was speaking during a visit to the BBC in London to view the work the corporation is doing as a member of his taskforce on the prevention of cyberbullying.
The Duke said: “We have seen that the technology that can allow you to develop an online community around a shared hobby or interest can also be used to organise violence.
“The new ways we have to access news from across the world are also allowing misinformation and conspiracy to pollute the public sphere. And the apps we use to make new friends can also allow bullies to follow their targets even after they have left the classroom or the playing field.”
William, who was with the Duchess of Cambridge, said he had been moved after meeting bereaved parents of bullied children who had taken their own lives.
Meanwhile, it emerged that at the 70th birthday party she had thrown at Buckingham Palace for the Prince of Wales, the Queen had paid a heartfelt tribute to her eldest son, describing him as a “dedicated and respected heir to the throne to stand comparison with any in history”.
The Queen rarely comments about her children but used the black-tie dinner in Charles’ honour to praise him as “his own man, passionate and creative”.
She described the event yesterday as “a great party”.