Factcheck.org covers this: http://www.factcheck.org/2016/02/donald-trump-and-the-iraq-war/"Donald Trump and the Iraq War", FactCheck.Org
On September 11, 2002:
Howard Stern asks Trump if he supports invading Iraq. Trump answers hesitantly. “Yeah, I guess so. You know, I wish it was, I wish the first time it was done correctly.”
Whether that is "support" is a semantic argument, so I just present the facts about what he said.
Factcheck.org couldn't find any more expressions of support for the war, and said:
Trump expressed concerns about the cost of the war soon after it started. If Trump did support the war, he turned on it quickly.
