Select your layer.
In top LAYER menu, select AUTO-TRACE
Make sure PREVIEW is checked.
Make sure APPLY TO NEW LAYER is checked.
Adjust settings 'til strokes are where you want them.
When done, turn off original (lower) layer.
Put a new light colored solid under the top layer.
Select top layer again.
Add a EFFECT>GENERATE>SCRIBBLE to that layer
Set it to SCRIBBLE>ALL MASKS
Change it to a dark color.
Reduce parameters until you get the stroke look you want.
A computer once beat me at chess, but it was no match for me at kick boxing. --Emo Philips