For one, circles in famous can be made simply by applying a 50% borderRadius property to any Surface element.
When it comes to arcs, there is no way in Famo.us that makes arcs easier to create. You will have to look into canvas, or SVG..
Here is an example of such in canvas..
http://wickedlysmart.com/how-to-make-a-pie-chart-with-html5s-canvas/