In the departures area, the passport control is before the security screening and on the far right, there is a designation for Elite/Elite Plus card holders - those are TK program levels. Don't recall if there was a Star Alliance Gold sign but I showed my Star Gold card and my boarding pass and they let me through. The other line was not that long, so I'm not sure if it was very helpful but it's nice to have the option. It was my first time doing it at IST - I usually just transfer when I've flown through there in the past, so never had to use it before.