Twitter CEO Dick Costolo has made a frank admission about his company's failure to deal with online bullying and harassment.

#Stop

Via internal memos acquired by The Verge, Costolo conveys to employees his concerns that bullying behaviour is turning new and existing users of Twitter.

"We suck at dealing with abuse and trolls on the platform and we've sucked at it for years.

"It's no secret and the rest of the world talks about it every day. We lose core user after core user by not addressing simple trolling issues that they face every day," Costolo wrote.

Action plan

The memos were in response to the case of journalist Lindy West, who was the subject of abuse after users created a Twitter account in the name of her recently deceased father in order to harass her.

Costolo admits to personally failing in this instance.