Whether you have thick or thin eyebrows can totally change the way others see your eyes. For example, sparse brows will make you look tired whereas well filled-in brows will give you an energetic and fresh look.
There are numerous products you can use to fill or draw in your eyebrows. You have to make sure the product you use is the same colour as your natural eyebrow. If it's too dark, it will be too obvious that your eyebrows are fake. After you are done filling your brows, you should add a coat of special eyebrow mascara to seal it in. If you can't find the right shade then you can use a transparent one.