Characters can post to the Social Media forum, they should note when they post and if this is a public or private/anonymous account. Private posts are often to specific people or groups, please note who can see such messages like specific people or say your followers or fans. Anonymous posts are considered to be accounts not tied to your name or identity but there could be a way to track who posted the message this will be a Technology check, contact the GM for the DC.
This is no single social media. But just a fun way to interact if you so choose. Players can always post to social media even if in an active thread during that time slot as long as it makes sense and they have access to the network.
if the post is an image/video you can attach a media or describe the scene in words. Whatever you prefer.