While I've never really heard of chocolate being an actual cause of acne, I can think of some things that chocolate might contain that can definitely exacerbate acne. For one thing, caffeine can trigger acne in some individuals and is found in some chocolate products. Caffeine increases adrenaline, which is also tied to an increase in testosterone, which could cause or worsen hormonal acne.
The major thing you want to look for is if the chocolate you are consuming contains dairy. Lactose intolerance was the cause of my acne, and as soon as I stopped consuming dairy my hormonal acne cleared up. Milk has a lot of hormones in it that can throw of your hormonal balance. I quickly realized that almost every chocolate product I consumed had dairy in it, although there is some dark or fine chocolates that don't contain dairy. Other than that I can't think of any other reason could cause hormonal acne, unless of course you're actually allergic to cocoa itself. That's a different story and you would need to get checked by a doctor for that kind of allergy. Best of luck to you!