British entrepreneur Nick D'Aloisio, who sold the mobile app Summly to Yahoo for $30m (£21.73m) at the age of 17, has sold his latest company to Twitter.

The Sphere group chat app was founded by Mr D'Aloisio and Tomas Halgas.

Sphere, which connects strangers interested in common topics, has been sold for an undisclosed amount and will close in November.

Its 20 or so staff will join Twitter to integrate their community features into the social network.

The company started as a question and answer app that allowed users to instantly chat to paid experts. At the end of 2018, almost 500,000 people were using that version of the platform.

However, Mr D'Aloisio said he found himself drawn to the community aspect of the app which brought strangers interested in the same topics together.

"What was interesting was that people were talking so often throughout the day, and it wasn't just talking to their friend on Facebook, but someone they had not met before about something they were interested in," he told the BBC.

As a result, the app slowly pivoted toward a focus on group chats.

Sphere's features include the ability to:

create multiple chats for a single group
send highlighted announcements so no-one in a group misses anything
send notifications to individuals or just those yet to read a message

"A lot of the messenger apps that exist are catered toward groups that already know each other, but with Sphere, the aim was to unlock new dynamics and bring together people around the world with shared interests."

Mr D'Aloisio said he was struck by the toxicity on platforms like Reddit, Facebook, Twitch and Twitter, which has been widely criticised about its handling of harassment and trolling.

Earlier this year, Twitter introduced a prompt that warns users about the tone of their message and asks if they would still like to post it.

And in September, the platform began testing its new safety mode which will flag accounts using hateful remarks, or those bombarding people with uninvited comments, and block them for seven days.

"They are as excited as us to try and figure out this problem around online communities," said Mr D'Aloisio. "It's not only a hugely interesting problem, but also a necessity.

"All groups have the potential to become genuine communities. But most groups suffer from problems in online communication that prevent community-building - things like awkward silences, conversations going off-topic, and vitriol.

"However, we learned over the past two years that a group can transform into a community if its members feel their participation is welcomed."

Twitter has been making efforts to expand and evolve its platform in recent months.

The company attempted to acquire audio rooms app Clubhouse before eventually going on to unveil its own similar feature, Twitter Spaces.

And in May, it bought news-reading start-up Scroll, which it says it will be rolling into its own services in future.