Caroline Criado-Perez helped lobby the Bank of England to make a woman, 19th century novelist Jane Austen, the new face on the country's 10 pound note, to defuse criticism that women were under-represented on the currency.
She was then "targeted repeatedly with rape threats" by ill-wishers objecting to her activity, according to an online petition, which called on Twitter to urgently add a 'report abuse' button to its service.
Some users proposed a one-day boycott of Twitter to protest against what they said was its failure to address the issue.
Twitter's General Manager for the UK Tony Wang promised to suspend all accounts found to be in breach of its rules.
"We take online abuse seriously," he wrote, saying the company was testing ways to simplify reporting of abuse.