When a friend gets dragged online, check on them privately before you pick a side publicly.

When a pile-on starts, the loud question in your head becomes what everyone will think of your response, while the person in the middle of it is alone with their phone. A public post, even one defending them, is partly about you, and it does not reach them the way one message does. They usually do not need a verdict yet. They need to know somebody saw it and is still around.

Send the message first. Plain works fine: you saw it, you are here, no reply needed. Anything public can wait until you know what would actually help.