I need help with my drug abuse?

i am a young teen who is having a problem with drug abuse. i started smoking weed when i was 12 and i am now struggling with an addiction to Methamphetamines. i am in a horrible situation because my parents think im this amazing child they dont even know ive smoked. but now ive goten to the point were i feel its been effecting me, my brain, my body, my grades. i dont know what to do because i cant just suddenly brake it to them. help:,( any advice can help me