The Skagit Valley Herald reported that teenagers who saw the status update alerted police.
Mount Vernon Police Lt. Chris Cammock said the teen was arrested Saturday.
Cammock said the boy has a history of police contact and is known to have anger issues and unpredictable behavior.
Police said commenters replied to the threats, saying they were not funny, but the teen allegedly said he wasn't kidding and that drugs were affecting his brain.
The boy is not enrolled in any Mount Vernon school.
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