I don't know. There's many people that do practically nothing in that regard and become mega hits overnight. Happens all the time in software. How many sales people were marketing facebook back in the day?
Facebook did things no one else did like allow you to import your hotmail contacts. They rolled out in small batches. At one point you needed a .edu email. The press was great. Facebook did so many things right marketing-wise in the beginning.. even now they always seem to be on the cusp of the next wave.
facebook type products are an outlier. It did not require traditional sales and marketing in the true sense as it did one thing right : creating a tool for college kids like me where I felt like part of the community. The idea was brilliant to keep it to college campuses only. I remember looking at fb for the first time (circa 2004 when it was only on college campuses) and going "wow, they have listed my dorm name" and immediately felt a personal connection. genius!! And of course, the UI was far more engaging than the incumbents. So fb was selling itself but most products don't.
Facebook practically implemented a worse version of MySpace. The only problem with MySpace was security issues which I think ultimately killed it in the end.
Almost every social media site wasn't marketed. MySpace didn't have marketing, neither did Facebook, neither did Twitter, Snapchat is still popular even though it struggles to make any money. Those are just the few that come to mind.
I don't have an exact percentage, and percentage wise its probably low when factoring in all the websites in existence.
