well iv lost 4 pounds since last Friday i just eat fruits for snakes and for breakfast oatmeal and lunch protein shake
unless you are on supps....and for some people even if you are...more than a pound a week is chewing up precious muscle....as a ypoung guy your metabolism should be raging...lifts some weights....play some sports...don't eat so much crap....no sugary drinks
If you're fat then like Z499 said, you'll see your upper abs start to define. Probably around 17-18% BF. Keep loosing and they'll all show eventually.
If you're skinny and have flat abs, start eating / doing compounds as suggested. If you're truly doing so already, consider that abs don't change substantially with training in appearance as there is a ton of connective tissue. The shape of your abs is largely genetic.