Here is a long list of the allegations that Turkey has been supporting ISIS and other Islamic groups in Syria. Each point is linked back to the original source. Some of the sources are more credible than others, and some of the allegations are a little vague, such as “supplied weapons to terror groups” or basically amount to Turkey has done a very poor job of securing its border with Syria, which could be an issue of competence rather than intent. Nevertheless, the list is long, and some of the allegations are very specific and if true clearly demonstrate support for ISIS.
http://www.huffingtonpost.com/david-l-phillips/research-paper-isis-turke_b_6128950.html
IR Theory & Practice 