Tracing with Paint Write-on?

Hi. I'm fairly new to AE and would appreciate if someone could give me any advice regarding this. I'm trying to do something I assume is a very basic task in AE but just cant get it to work and cant find assistance in the painting section of the manual on this. In Photoshop Elements, I make a line drawing of a face on a transparent background. I import this to AE as well as a blank transparent image. I move these two layers to the timeline.On the blank transparent layer...my goal is to trace the underlying line drawing using the Paint-write-on tool so that I end up with an animation of the face being drawn line by line by using the line drawing underneath as a guide for the paint-write-on tool.However.....when I select the blank layer...I cannot see the line drawing layer underneath to trace from. Is it not possible to trace an image in AE with the paint-write-on tool? I assumed this would be one of its common uses.If this cannot be done....is there some alternative method to achieve the final goal? Thanks.