To change the thumb image you can simply create the following style and apply it to your ScrollView:
where scroller_thumb is your custom image for the scroller thumb.
also note the following attributes:
Now, in order to put the thin line you want under the scroller, simply add an image view containing the line image, to the direct child of the ScrollView (RelativeLayout child as a direct child for the ScrollView will allow you to position the image on the right side of the view - so this is would have been my choice).
and that's it.