I recently told my parents about my SI. Actually, I didn't really tell them. I told somebody who told them for me. Anyways, my mom and I had this conversation and that was pretty much it. Things haven't changed at all. I'm not seeking professional help, and my parents haven't asked me too. I still SI (though I'm not sure my parents know that).
About the only thing different is that they walk on eggshells around me. I really wish I hadn't told them because it really hasn't done much for me. Things aren't getting better (despite everyone telling me that if I hold out for x length of time things will improve), and I don't know how much longer I can put up with that.
It's really hard to reach out for help when I feel like no good will come of it.
First I want to say welcome to TeenHelp!
In order to get help for self harm, you have to want the help and ask for the help, because it seems your parents aren't asking you if you want help, they probably don't know how much they should ask you for fear they ask you to much and you continue SI. That or they don't know how to get you help, in this case, you can tell them you want to talk to a professional counselor for help with your SI and you can tell them that getting help is very important to you and that you feel as though talking with someone will be the best way for you to get help.
It will be scary at first, having to begin trusting and opening up to a therapist/counselor, but it will be worth it to get what's causing you to SI out in the open and dealt with. Quitting SI isn't something that just happens, it takes time and it's okay to slip up during the process of quitting, try setting goals for yourself and once you meet those goals, or pass them, reward yourself for not SI and extend the goal even farther. For example: Your first goal is a week, you reach eight days, reward yourself and set a goal of another week or ten days or whatever works for you, keep setting goals and rewarding yourself, if you don't meet one of your goals, that's okay, just start back at the beginning and work your way up again.
Also, you should try looking at the alternatives thread, there are a lot of great alternatives in there. The thread is at www.teenhelp.org/alternatives If some of the alternatives don't work for you, don't give up on them all, somethings don't work for some people and it might take time finding an alternative that works for you. If after a while one doesn't help, try something else.
I hope I have helped, if you ever need anything, you can PM me and I'll be glad to help. You can do this! Good luck! All of TH is here for you!