Does masturbating cause acne in your face?

No. It would be difficult to find a control group. Perspiring may make it more visible after you enjoy your body, but it's not the cause. It's actually moot since all acne is manageable nowadays with scientific Rx. If topical benzoyl peroxide has not cleared you in two weeks get with your physician who can add something that will.
No. It may be the other way around. A relative increase in your testosterone level may cause acne outbreaks to worsen while increasing your libido and urge to masturbate. However that is only a postulate and not proven.