All you have to do is search and see if your neighborhood or city already has some kind of yard sale group. I am a member of 4. The one shown below is the biggest one in my city, but I am also a member of specific area yard sales that are in my general vicinity.
I had to request membership, but other groups may be different. If your city or town doesn't have a yard sale group, maybe you could make one! It's run by normal people and there are usually some rules.
So here is what the screen looks like from my phone. People are posting a listing like every 10 seconds on here and you just scroll.
The ettiquette for this particular yard sale group is that you write "interested" if you wish to buy the item and then arrange meeting details with the seller.
A few pointers...
Unless you need to pick a large item up, meet the buyer/seller in a PUBLIC place. I meet people in Target/Wal-Mart/Kroger parking lots.
Similar to eBay, post your items when people are more likely to be on facebook. In the evenings or on weekends.
Happy Shopping & Selling! If you have any questions I will be more than happy to answer or give advice!