Amanda Abbington has revealed she and former partner Martin Freeman were once sent photographs of baseball bats wrapped in barbed wire.
The actress, who starred alongside then-partner Freeman in Sherlock, said she felt "sick and terrified" and took the pictures to the police.
Abbington, 46, said she had seen the "worst" of social media.
"I hope people will realise we have to treat people carefully," she said. "Social media can be a great forum, but it can also be a platform from which people bully.
"I think there should be a rule to say you have to be listed as your real identity on social media and that you can't hide behind an anonymous one. You can't say those things to people."
She went on to detail her own experience, describing it as a "really horrible time".
"I've experienced some of it myself for example, when my ex-partner joined Sherlock we got pictures of baseball bats with barbed wire wrapped around them sent to us," she said.
"It made me feel sick and terrified.
"We took the evidence to the police - it was a really horrible time.
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"So I've had some of the worst of it and I hope people will realise how horrible it can be."
Abbington appeared to delete her Twitter account earlier this year, but is still active on Instagram.
She is now playing the mother of a young man who finds fame on reality television in the BBC Three film Make Me Famous, which is written by Reggie Yates.