Hmmm... I've had a look at the website quoted; and I admit that there are some quite good graphics there. But, I imagine that there is quite a small requirement for those imagines from an external source. Surely a majority of the people who need those sorts of graphics have their own in-house facilities?
Your question raises further questions in my mind:
* Who is _your_ target audience and do they need your graphics?
* How are the sales for other people in the market.
* How do you imagine a Facebook presence will increase your sales?
* Does your target audience know you ave a blog?
* Have you thought of freebies to get some people interested?
* Have you done some research on end users and sent a few free samples off to them?
In any free-lance industry, you can't sit back and hope that people might see your work in passing; you've got to let the audience know who and where you are - and remind them constantly. The free-lance market is too tough and competitive. My 'ex' has a son-in-law who is a known 'comic' artist and he quite often struggles to find work - even though he is known.
Sorry that it all sounds rather negative; but I'm afraid things all too often are in any free-lance market.