BBC Radio 5 live presenter Richard Bacon has revealed that he has suffered two years of anonymous abuse directed at him, his wife and his baby son.
Bacon has complained to the police, and tried to track down his abuser for a BBC Three documentary on abusive "trolls": The Anti-Social Network.
He said he wanted to know how criticism of his work "could go to contacting my family and tweeting about my baby".
He said it was time to stand up to trolls and highlight internet bullying.
"You have got to try and work out where critical comment crosses over into harassment," he said.
"Under freedom of speech people can criticise you and slag you off, it's their right to do that."
But he added that it can become "deeply personal, obsessive and weird."
Bacon, 36, said the line had been crossed when criticism about his radio show turned into abuse about his wife, his mother and five-month-old son Arthur.
The former Blue Peter presenter said he had originally tried to meet the troll but was advised by a psychologist and the police to make an official complaint instead.
He said: "What I have been through isn't that bad, really; it's been distressing for my family but personally as a broadcaster it's something I know how to deal with."
Much more disturbing, he said, were the actions of "RIP trolls" who posted offensive messages on tribute sites.
While filming The Anti-Social Network, Bacon met the parents of the late Tom Mullaney, from Bournville, Birmingham, who died aged 15 and whose tribute site was hit by trolls who left offensive messages.
"They see these nice tributes, then they also see these weird sexual, violent comment and imagery," he said.
"For people who don't even understand Facebook in the first place, as well as being upsetting and prolonging their grief, it's confusing."
He said some of the trolls would "themselves be deserving of sympathy - but that doesn't mean we shouldn't tackle them".
"It's time to stand up to them, it's time to either expose them or, if you're a victim, go to the police."
The Anti-Social Network will be shown at 2100 GMT on Monday night on BBC Three.