Can a bald spot be formed by taking mass gainer supplements or because of stress? (Photo)

You need to be evaluated by a professional first of all. I have not heard of supplements causing hair loss. Steroids such as testosterone can accelerate hair loss in male pattern balding. 

I see the thinning you are referring to. I recommend getting a consultation with a cosmetic dermatologist with experience for hair growth. There are some great options for hair restoration and maintenance like prp injections which can stimulate hair growth. Hope this helps.

This area needs to be examined up close if one wishes the diagnosis. There are no other ways around it. Be sure to see your physician.