If not, you should. At least 25% (if not more) of my sales come from social websites. Some will even pay you to share pictures and links (like items in your Etsy / ArtFire shops) Besides you gain a trust among the people, thus they are more likely to purchase from you. Pretty sweet when you can get paid to show off your products!
Here's a couple of the sites I belong to. (and yes, I do get credit for referring people too)