Why don't girls find me attractive or notice me?

I feel empty and depressed. It's like when I go places and I see cute girls they never notice me. It's like am a ghosts to them. They always look at my brother. My family and friends tell me I'm not ugly. If I'm not ugly then why don't girls look at me or notice me. I try to lift weights and get in better shape so girls can notice me. But it didn't help. I'm 16 never kissed a girl, never held hands with a girl. Sometimes I feel like giving up and wishing I was never born. I see my brother and my friends getting cute girls but I can't get anyone. You know I wanna have a cute girl. I just feel like killing myself. I just give up with life.
Why don't girls find me attractive or notice me?
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