Vaseline can help with acne scars after you've gotten rid of the acne first.
To get rid of the acne you can apply some lemon juice to the acne and let it dry on the acne and then wash the lemon juice off your face after it dries.
Then repeat that process everyday at least 2 times per day and the acne should go away and then apply the petroleum jelly over the acne scars to help seal in moisture and overtime the acne scars should start to fade.
You can also get rid of your acne by applying some apple cider vinegar to the acne just like you would the lemon juice and it too will help get rid of your acne.
Or you can use toothpaste to get rid of the acne and then let the toothpaste sit on the acne until it tingles.