I hope you're not using bread yeast. The yeast this is talking about is "nutritional yeast". You can find it at any health food store. It is LOADED with all of the B vitamins and is high in protein as well!
I also read that the food that has the highest concentration of B12 is yeast. So I made up a slurry of yeast, and also gave this chick the baby vitamins Polyvisol and vitamin B12 liquid with some egg yoke which is also a good source of B12.