You may want to reply back to the person or send them a private message where you encourage them to seek help. Consider sending them the numbers to a suicide hotline to talk with a trained suicide counselor.
[header] How to react if you see a suicidal post on facebook [title] Comment and encourage the person to seek help. [step] Many people ignore suicidal social media posts for various reasons. However, social media suicide threats should be considered as serious as any other suicide threat.