The group told Mr Key of the "deep dissatisfaction" families had with the inquest process, calling the experience "abusive" and saying the court routinely ignored evidence from people who knew suicide victims best.
They also raised concerns that families were actively discouraged from participating in investigations into the deaths of their loved ones.
The group called on Mr Key to consider a Royal Commission of Inquiry into suicide, which he said he would consider.
Mr Key has already indicated his commitment to tackling the issue, having instructed his department to launch a review of the youth suicide rate, which is the highest per-capita in the developed world for girls and the third highest for boys.
Casper's suicide prevention strategy presented evidence that social interventions were more effective at addressing suicide risk than the mental health model. The group said that approach could save the Government money while saving lives.
"Millions of dollars are spent annually on mental health services and pharmaceuticals which research has shown increase rather than decrease suicide deaths," Ms Bradshaw said. Ministry of Justice figures last month showed more than 550 New Zealanders had killed themselves since July last year - 12.65 suicide deaths per 100,000 people - slightly up on the past three years.