No. Not at all. Have you not read what is commonly spouted on the internet? You have to be 100% illiterate to not understand that this was tasteless sarcasm.

This doesn't mean I think it is funny or that I agree with it, but calling the police over a joke is pointless and irresponsible.

However, this is like putting out a candle with a fire hose.

Every teen has at one occasion thought: I feel like killing [everyone in school, my team, my so-called friends, my brother, my ...]. Writing such a thought down gives it extra power and a screen doesn't confront you with a person and make it easy to misjudge whether you can press 'send'.

Monitoring that speech and acting on it, directly by the government or indirectly via 'concerned citizens': that way lies police state insanity.

So the answer is emphatically, decisively: no. You should not want to report this.

By these standards, you'd have to arrest every teenager in America eventually. That isn't an exaggeration.