My husband left with no warning and totally cut ties
My husband walked out on me and our 3 kids 4 yrs. ago, no warning no explanation, no communication. He filed for divorce 9 mos. after he left, never helped support us after the day he suddenly announced he was leaving. Rarely sees our kids, it's like we don't exist. I was married to this man for 20 yrs., he never told me he wanted a divorce. After he left he never spoke to me again, just a regular Wed. Night and suddenly he makes his announcement, exits and I'm a single parent with no income. It's as if the kids belong only to me, sorry but the whole family thing just wasn't working for him? We are all hurt and confused, he is like a total stranger.
As it has been four years, and he has not supported you, I suggest you either go to your government if it has a 'dead beat dad' kind of program where they will find him and garnish his wages, or you take him to court to force him to pay support.
As for his involvement with your kids, I don't know of anything you can do to change that, although the kids might write him a letter to tell him how much they hurt that he doesn't seem to have time for them.