While research have not proven that wearing a cap causes hair loss, it will certainly NOT help with your hair loss. Like you, hair follicles need to breathe.
The most common form of baldness, is medically known as is Androgenetic Alopecia and the condition has been attributed to male hormones affected by genetic inheritance.The triggering hormone is DHT (testosterone and 5-alpha-reductase), a naturally occurring hormone that helps in sexual development. Do some research on DHT and you will learn that there are products out there (like MiN New York's [MiN.com] DHT Cleansing System) can help you proactively address/block this hormone to deter hair loss.
Wearing a cap often will likely cause your hair follicles to be blocked by sweat, natural oils and proteins. Avoid topping your hair with lots of styling products. Cut back on gels, sprays, and mousses, which can all build up on your scalp, making it even oilier.