As others have pointed out, successful trading has to be mutually beneficial. It also usually requires that you do the work. If you simply post X player is available, you are asking others to do the work for you, which lowers the probability of a trade substantially. I usually follow these basic steps (and I realize they are not exactly rocket science):
Step 1: Decide what position you want to upgrade.
Step 2: Decide what position you are deep at.
Step 3: Look through the rosters to find a player with opposite needs. Often times I don't find an owner with opposite needs--in that case, I generally don't proceed further.
If you find the right owner, they will be interested if you can provide them a legitimate upgrade at their weak position. The old adage "you have to give up something to get something" comes into play here. If I am deep at a position, I will often dangle the player who is generally MORE liked in the trade. For example, I was deep at QB (Brees, Warner, Campbell) in one league and weak at WR (Patten was my WR2--thank you Colston/Burleson/Galloway). There was another owner who was in the opposite situation, so I offered Brees for Owens. Note I like Brees more than Warner, but my overall output increased much more replacing Patten with Ownes than my QB dropped going from Brees to Warner.
The reason most trades don't get done is that both owners want a costless upgrade (everyone wants to trade a guy on their bench for a guy who will start). Those trades are great and occasionally happen, but most of the time you have to take a minor step back at one position to take a big step forward at another.