On my boob i have a big 3d vein circuling around my areola. but its more closer to my nipple. is it harmful to put makeup coverup on it? im 16.

No, it's okay: Such veins are normal and if the appearance bothers you, i can cover it with make up.

No harm: It is very common to see prominent mammary vessels. This is purely a cosmetic issue. Only you, perhaps a parent, and any sex partner you have will see this. If you wish -- for instance, during a photo shoot -- it is absolutely safe to put cover-up on it. Otherwise, your breast will be covered, and it would not be necessary to use make-up.