To fill in your brow, you could use a brow powder or mascara, but I find that a brow pencil allows for more control in creating a straight line. Go a few shades lighter than your actual hair color - unless you're blonde, in which case you should go with a dark-blonde or light-brown shade. If you have black hair, do not use a black eyebrow pencil. Instead, use a gray shade or dark brown; I promise it won't look like you're aging in the eyebrow. It'll create a softer look while still adding definition to your brows.
As you could see, this Holika Holika Wonder Drawing Eyebrow pencil cost at Php552.00 (regular price) and now for only Php484.00 (as of this writing) from ALTHEA