The front blade of a throwing knife can be designed in a shape of leaf, diamond or zero frills. A good throwing knife posses the two important things. First is the weight (it should be light) and Second is it should not be sharp. You can simply go for simple, round shapes without spikes one.
maybe like the popular Gil Hibben throwers. They where a 3 knife set
Also, Look up Bobby Branton. Professional Knife thrower. Saw his Demo at Blade a few times