Social media firms should make it easier to report potential illegal abuse to the police, the public standards watchdog said.
The Committee on Standards in Public Life said Twitter, Facebook and Google had a responsibility to their users to set out how to “escalate any credible threats they receive”.
The criticism formed part of a report on progress in tackling intimidation aimed at people in public life.
Since its initial report in 2017, the committee said all three social media companies now had measures in place to protect users from intimidation and harassment.
But “neither Twitter, Facebook or Google appear to publish data on the time it takes to remove reported content”.
That information was needed to “help satisfy the committee that social media companies are able to make decisions quickly and consistently on the takedown of intimidatory content”.
All three firms established temporary teams during the 2019 election to protect the integrity of content and tackle potential threats and challenges.
Facebook has established a permanent reporting channel for MPs to flag abuse or threatening content, the committee said.
But the committee said it was disappointed that social media companies had not done more to help users escalate potential illegal online activity to the police”.
The report said: “It remains our view that social media companies have a responsibility to advise their users about how to escalate any credible threats they receive.”
Former MI5 chief Lord Evans, the committee’s chairman, said: “We are especially pleased to see social media companies doing more to protect users from intimidation online, though there remains more to do and at a greater pace.
“We were pleased that Twitter, Facebook and Google set up temporary election teams in 2019 to respond quickly to potential threats and challenges, including intimidation.
“We remain disappointed that these companies have not yet revised their tools that enable users to escalate potential illegal content online to the police.”
In its 2017 report the committee had called on political parties to show leadership and do more to protect candidates from intimidation.
The committee said parties had made progress in a number of key areas but there is “still work to be done”.
All the parties represented at Westminster now have codes of conduct setting out minimum standards of behaviour and internal disciplinary processes to deal with breaches.
The committee called for parties to provide data on complaints relating to intimidation.
Lord Evans said the murder of Labour MP Jo Cox in 2016 was a “terrible example” of what could happen if intimidation of figures in public life was not addressed.
“The Committee will never forget some of the personal stories they heard about the abuse and intimidation individuals and their families have suffered, simply because they are involved in public life.
“The murder of Jo Cox MP was the most terrible example of what can happen at the extreme, if intimidatory behaviour is not addressed.
“We already know intimidation puts good people off taking part in public life, particularly women and those from ethnic minority backgrounds.
“That is something we should all care deeply about, whatever party we choose to vote for. Intimidation and abuse have no place in a healthy democracy.”