I filed a missing persons report on my daughter when my daughter was 19 and told them of her threats to kill herself.
The response was that it is not illegal to go missing. If she happened to come up up on their radar, the best they could do for her would be to take her to an ER for an evaluation and if necessary, stabilization. And that assumed she showed on the radar in the same county.
In otherwords, they do not go out looking for an adult who has gone missing unless foul play is a serious consideration.
State laws vary in regards to involuntary treatment. It's no coincidence that addiction treatment centers have the most experience with this because it's a business opportunity.
If your words had the power to compel him to harm himself, they would also have the power to cure him. If only that were true. If only.....