Threads, launched by Meta on Wednesday, became the fastest social platform to reach the 100 million user milestone.

Meta CEO Mark Zuckerberg announced the Twitter competitor's achievement in a post on Monday, saying, "that’s mostly organic demand and we haven’t even turned on many promotions yet. Can’t believe it’s only been 5 days!” 

Threads is a text-based app that allows users to connect with their close friends and family. It is integrated with Instagram, so users can sign up with their existing handles and retain their following.

Concerns over how Twitter owner Elon Musk handles content moderation on the platform are driving people and brands to leave the platform. Some smaller players like decentralized social app Mastodon and Jack Dorsey-backed Bluesky are offering alternative options for Twitter users but haven't yet made a splash like Threads.

The app's rapid growth appears to have come at a cost for Twitter. Matthew Prince, CEO of Cloudflare, shared a screenshot on Twitter on Sunday showing that traffic on the platform was "tanking."

Also, according to Similarweb, a data company that specializes in web analytics, web traffic to Twitter was down 5% for the first two full days Threads was generally available compared with the previous week. The company said Twitter's web traffic is down 11% compared with the same days in 2022.

Musk appears to have expressed some concern about Threads, with his lawyer, Alex Spiro, writing to Meta accusing the company of "unlawful misappropriation" of trade secrets.