I don't know the full story, but I think that it was mostly marketed through word of mouth in the early days.
You've probably heard about the guy who bought a couple of pizza's for over 10.000 BTC? This was one of the first 'high value' transactions here on the forum.
People just negotiated the price for goods and services here on the forum, that's how the early Bitcoin price was determined, if I'm correct.
You can read a bit about Bitcoin's price history here:
https://en.wikipedia.org/wiki/History_of_bitcoin#Prices_and_value_history