I just learned that Noël Wells, a.k.a. "the token woman" among the new members of Saturday Night Live this year, sort of came from youtube originally. She did a series of fake Zooey Deschanel videos back in 2010 that got a slight bit of traction, but not much. (The first ep has 350K views, i bet a good chunk of that came after she made it to SNL).
In 2013 she did a three-episode series called Manic Pixie Nightmare Girl. They only got between 15-45K views each (in descending order as usual). But the style of comedy here is clearly the sort of sketch comedy that will work on SNL, but doesn't really work on youtube in terms of getting an audience. I laughed at em at least.