Bumble And Bumble Thickening Spray for thin hair?

my hair has gone thin over time and whenever i try tying it up in a ponytail ,there is not much hair at the back of my head that i can feel.my hair feels very light and breaks off easily if i comb my hair continously.this has made me really lose confidence as when i see other girls who are my age of twenty seven have have  thick and healthy hair .then  my friend told me that if i cannot get thick hair then i can very well use Bumble And Bumble Thickening Spray to add volume to my hair and gives it wieght.where in the hair area do you need to apply Bumble And Bumble Thickening Spray in order to get thick hair?