You have to render with maya software as mental ray will not render strokes. You can select the stroke and then goto modify and convert pfx to polys should work. Another option to render with mental ray is to enable contour rendering you can then adjust the shader so it puts an outline around the object. If you use the link to my website there is some akira stuffs using this technique. I can give you a rough idea of the workflow for this if you need it.

Hope this helps,

Leon