Okay, just speaking from my gut without any data or experience to back it up --
It seems to me finding someone to buy your art thru advertising on the web is the longest of long shots. The tiny ad budget most of us have would make less impact than a grain of sand has on the beach. And not sure that many people buy art based on advertisements anyway.
It seems what best works for artists is word of mouth(or I should say word of post) getting some level of viral attention. How exactly you do that is the big question. Many have tried, few have succeeded. Blogging, youtubes, forums, facebook, instagram etc. are all fishing lures you can put out and see what bites.
Lately I'm thinking - "what can I do in the real world that could bounce back to the digital world and make some impact."
An example. A few years back during the bank-made Depression, there was an L.A. based artist that set up easel and did plein-aire paintings in front of banks - but painting them on fire. He didn't do anything other than paint in front of a bank. He had no agenda other than making a painting. But people saw him and there was such outrage at the time that it got picked up by the local paper, and then the national news, and then all over the web -- and he sold A LOT of paintings and became established.
I truly believe if he had sat at home, made the bank painting and then posted it to the web, it would have been drowned. So in my mind "viral" is the key, but don't forget about the real world as a way to get there.