Seeking advice on how to seek help for Depression. Please read description.

I'm 18 and I believe I have been suffering from depression for the past six years. I want help but I don't know how to ask for it. It scares me to even think about telling someone close to me. Can someone give me advice about how I can deal with this and seek help. I really need help. It's affecting my grades, my social life, my health preventing me from getting a job, it's messing up my ambitions for my future and I can't take it anymore. I wish I would have sought out help sooner.!! This is not a ploy for attention I really need help and want only serious answers....