I need serious help please someone help me!?

ive felt really depressed lately and my friends have started to notice how do i stop feeling this depressed i often have thoughts abou si and i need help! ive told one of my friends about sn attempt i made to hurt myself but she just kind of laughed like i was joking. i dont know what to do any more ive told my sister to that i felt depressed and she also just kind of shook it off and told me to listen to some music. help please