Twitch is a live video streaming platform on which creators broadcast live video to viewers, who can follow channels and chat in real time. It launched in 2011 as a spin-off of Justin.tv and is operated by Twitch Interactive, Inc., a subsidiary of Amazon. The service is still active.
Twitch Interactive is based in San Francisco, California, and as an Amazon subsidiary it is subject to US ownership and US law. Wikipedia notes that Twitch added servers in Europe in 2013 to reduce lag, but the sources used did not state where customer personal data is stored or processed. Twitch is a proprietary service and not open source. For a European organisation, the main points are the US parent company and the unconfirmed data-storage location, so use should be assessed against its own requirements.