I don't think shea butter itself will help increase boobs. I think if u mix it with a little fenugreek extract or lavendar oil, it may help some.
But shea butter is good for preventing stretch marks and it makes a good massage cream.
Its a good idea to start preventing stretch marks if your gonna grow ur breasts.
Try using fish oil capsules on your boobs. I'm reading on another forum that some girls are trying that and its helping a little.
Flax oil I don't know about.Some articles say that it is good for NBE.You can try it and see.As far as shea butter,the shea butter in itself will not make breasts grow,but will keep them moisturized and supple.The massages will help you grow.I have been using Palmer's cocoa butter lotion with collagen,elastin,Vit E,and shea butter for my mid-day massage.I personally got it for the collagen(very beneficial to NBE),along with minimizing my light stretch marks,as they are smack on top of my breasts now due to growth.Not very noticible,but they bother me.I have read articles that states cocoa butter with the use of Vit E has proven permanent growth and results.If you are going to do massage,give this lotion a try.