I was recently at a Microsoft heavy tech conference and spoke to at least 50 .Net developers. Anyone who also did front end did so in Angular. I was surprised at how popular it is!
The Stack Overflow developer survey showed that React and Angular are neck to neck so there's obviously a lot of people who use it.
However, you can see just how popular React is by number of npm packages that depend on it: https://github.com/facebook/react