An American firm has bought the popular question-and-answer site Ask.fm. It has 180 million regular monthly users, but has also previously suffered controversy after some teenagers experienced "cyberbullying".

IAC - which already owns the dating app Tinder and Ask.com - has not revealed the terms of the takeover.

The move is the first significant push into social networking for Ask.com, which was more popularly known as AskJeeves, when it began as a search engine back in 1995.

Ask.fm says it reaches 180 million monthly unique users in more than 150 countries.

The CEO of Ask.com, Doug Leeds, has said the group will now add new safety tools and moderators.

"The plan for unlocking its true potential will focus on making the experience even more engaging, while significantly increasing the investment in safety," Mr Leeds said.

The company has also brought on Catherine Teitelbaum to work as their chief trust and safety officer. The New York Times says Ms Teitlebaum was previously a director of global safety and product policy for Yahoo.

While digital safety expert Annie Mullins will lead Ask.fm safety efforts in Europe. 

Ask.fm generates an estimated 20,000 questions per minute, with approximately 45% of its mobile monthly active users logging in daily.

To date, the mobile app has been downloaded more than 40 million times.

Ask.com partnered with New York Attorney-General Eric Schneiderman and Maryland Attorney-General Doug Gansler in the creation of parallel agreements.

"Today's agreement shows once again that regulators can work with technology companies both to encourage innovation and protect consumers, including our youngest digital citizens," said Attorney-General Schneiderman in a statement.

"I applaud Ask.com's leadership in working with our office to design a program that protects Ask.fm users from cyberbullying and other harmful content. We would hope that this collaboration serves as a useful model for other companies in the digital space," he added.