If you are worried about something that a friend has posted on social media and you think they may come to harm then there are things you can do.
Instagram and Facebook both have a suicide prevention tool that lets you report a post to them, and they will then contact your friend offering them help. This might be giving the details of the Samaritans helpline for example.
Currently there’s no tool like this on Snapchat, so you could talk to a trusted adult for advice if you don’t want to say anything to your friend, or if you’re really worried call 999.
It can be hard to know what to say when friends come to you with problems or when you think they may be struggling.
There's a poster with advice on what to do if you're worried about a friend here.