I’ve actually done just this effect for the job i’m currently working at. The best way I found was to use the pen tool and semi mask off the drawing. What I mean by semi mask is to trace the outlines, but not with one continuous stroke. Trace chunks of the outline of the shape, in a order that would be believable as the order you drew it in.
Once you have those, use Effect>Generate>Stroke. In the options, check All Masks and Stroke sequentially, then go to the bottom and change Paint Style to Reveal Originial Image. From there just keyframe the End percentage. You may need to adjust the brush size, depending on the size of your drawing, but that should do it.
Hope this helps.
Till