Fortified foods, such as some brands of cereal, nutritional yeast, soymilk, or veggie "meats" are good non-animal sources. Check labels to discover other products that are fortified with vitamin B12. Tempeh and sea vegetables are not reliable sources of vitamin B12.
To be on the safe side, if you do not consume dairy products, eggs, or fortified foods regularly, you should take a non-animal derived supplement.
We store between two and five milligrams of vitamin B12 in our bodies and only excrete a small fraction of this each day. Over time, vitamin B12 deficiency can develop if stores are not replenished from the diet or supplements. The RDA for adults for vitamin B12 is 2.4 micrograms daily.