I'm lucky enough to have been played by a YouTuber with 2 million subscribers (wow now he's at 11 million), the video got 1.1 million views. It is tough to gauge if the game got traffic from the video, because the game was already #1 on a website for 24 hours before their video came out. Looking at the video, they never bothered to have a link to the game below. It's just all links to their social media.
Looks like the game was still getting 1,000 demo downloads a month for several months after release, with a 1:2 download to page view ratio. The #1 method for people finding the game was a direct link (53% of players found it via that method). The #2 method was the website itself with 35% or so, and the lowest method was 6% finding it via YouTube, so someone linked the game. Probably in the comments of the 1.1 million viewed video.
Does that mean people had to watch the video, then visit the website, and look for the game? Or did people just see my game was #1 that first day and flood in from there? Perhaps the 1:2 download to page view means people saw the video, and they know they're interested in the game.
To continue this, perhaps a better analysis is "the next game," after the one that got all the attention. The next game had a lot of minor attention. YouTubers with 10 - 100 subscribers. That game had 33% of the traffic that the previous game had, with a 1:4 download to page view ratio. 90% of the game's traffic came from the website itself. This could mean that the previous game did get a bump from the popular YouTuber.