I've been thinking of starting one again. But maybe not let myself label it with something so definitive; just a very private notebook that consists of all my venting. Had one as a teen, but got tired of my hand getting carpal tunnel from writing in it so much. Then I ripped it up to shreds two years later. I can also be quite irresponsible with things like that, I'm tired of having them found. But, writing down your thoughts really does give some sense of relief or clarity.

Do you or have you had one?
If so, does it help in any way?
And do you have some sort of method? (i.e. consistent basis or for need-only purposes)
If not, why not and are you going to start?
Paper or digital?

i did in like 5th or 6th grade, but then my brother found it and read it aloud during family reunion and never again

Not really, but I have a song book.

I have had a diary since I was 7.

I write lyrics. It's kind of a journal when it becomes personal.

I also use one of my tumblrs as a form of a memoir.

Well, I have a blog but I don't get to update it everyday
But I also have a planner but I only use that to list down things that happened that day or future stuff I have to take care of.

No but I was thinking about writing one yesterday.

No. I used to all the time though when I was in middle school/beginning of high school. I could never keep it up for very long though. I feel weird knowing that nobody is going to read what I'm writing so it feels kind of useless? I wish I had more motivation to keep one.