Reading about suicide in the news is incomparable to the kind of direct intervention I'm talking about. As john_fushi commented[1], the best thing you can do is talk about it and his suggestion of calling your local suicide helpline for advice is an excellent one.
On a personal level, I've found that talking frankly about suicide greatly reduces my desire to act on any suicidal feelings. This effect is greatest when talking face to face with somebody I know and trust.
However, worrying about whether or not somebody trusts you should NOT stop you from intervening. If somebody shows a desire to listen and help my in such a situation I'll have a much greater level of trust in them than I did before, even if they were previously a complete stranger or somebody I dislike.
[1] https://news.ycombinator.com/item?id=7228997