Facebook, Google, Apple, BT and Microsoft will all give evidence to the Independent Inquiry into Child Sexual Abuse over the next 10 days.
Alexis Jay, who chairs the inquiry, said it would consider "the adequacy of the response of the internet industry" to the online facilitation of abuse.
The hearing opened earlier on Monday.
Opening the proceedings, legal counsel Jacqueline Carey outlined some harrowing examples of child grooming online and its devastating impact on their lives.
She also told the inquiry:
A UK police database contained more than 13 million indecent images of children
In 2018, the Internet Watch Foundation had received 105,000 reports of child sexual abuse
William Chapman, representing three victims of online abuse - two of whom are brother and sister - told the inquiry "the largest tech firms are failing" to prevent children at risk of sexual abuse.
"Is it really beyond the wealth and wit of these technology companies to prevent and detect child sexual abuse on their platforms?" he said.
"Or is there something incompatible with their commercial objectives... their culture and ideology... that makes them bridle at the necessary steps to curb this modern scourge?"
Ms Carey spoke of some of the measures technology companies had implemented, including the hashing of images, which provides a digital fingerprint of them so they can be identified if circulated.
One victim, speaking anonymously, said her abuser had contacted her via Facebook and Twitter messages but she had not reported it to the social networks.
"You just think, I'm on my own, how can they help?" she said.
At the weekend, Chief Constable Simon Bailey called for a boycott of social media.