the first place you should start is the Free The West Memphis 3 site.
This case is immense, and the main ammunition of true supporters is knowledge. Familiarize yourself with the case by reading Blood of Innocents and Devil's Knot; take advantage of the huge document/evidence archive available here. Watch Paradise Lost and Paradise Lost: Revelations, read courtroom transcripts. Stay focused and help turn the tide from rumor and fear to facts and knowledge, and eventually, freedom.