We forecast that 37.5 million people in the US will watch streaming video on Twitch at least monthly in 2020, meaning the video streaming platform will reach 15.5% of US digital video viewers this year. At its current pace, Twitch will surpass 40 million US users by the end of 2021, according to our first ever forecast for the platform.

We define Twitch viewers as internet users of any age who watch Twitch content on any device at least once per month.

"Twitch is by far the largest platform for streaming video game content, well ahead of YouTube, Mixer and Facebook Gaming," said eMarketer forecasting analyst Peter Vahle. "As the pioneer in this space, Twitch has built a loyal and engaged audience by allowing viewers to directly interact with their favorite streamers."

Twitch will grow by 14.3% this year. But as Twitch loses share to competitors like YouTube, Mixer and Facebook Gaming, that growth will slow.

"Twitch, which is owned by Amazon, hosts streaming video content primarily focused on video games, including live streamed broadcasts. [Live and non-live content] is now too big for the internet giants to ignore," Vahle said. "The big platforms, owned by the likes of Facebook, Google and Microsoft, are competing to sign big deals with popular streamers and esports leagues. Twitch will have to find ways to encourage streamers, viewers and advertisers to stay on its platform now that other attractive options exist."

He added that Twitch can continue to grow its platform through nongaming content, which began driving significant traffic last year. The platform is designed for live streaming video and streamer/viewer interaction and "these features are certainly intriguing to content creators outside of gaming," he said.