The best website to check is the Man in Seat 61 website. That's how I figured out how to travel via train through Turkey, and it covers all over Europe. The other great thing about it is that it helps you navigate though the Turkish TCDD website which is entirely in Turkish and sometimes the translator doesn't work. The Man in Seat 61 site for Turkey is http://www.seat61.com/Turkey.htm. Likewise the Turkish national train system website is http://www.tcdd.gov.tr/. At the top of the page is a tab that says English that should translate the page.
