I\'ve seen other topics like this: launch facebook app from other app and tried some of the URIs listed there, but I can\'t figure out how to start the facebook chat with a
startActivity(new Intent(Intent.ACTION_VIEW,
Uri.parse("fb://messaging/" + userId)));
found it here: https://developers.facebook.com/docs/messenger-platform/discovery/m-me-links#format
http://m.me/{#user_id}
you can use this URI to open messaging with a friend with known id.
You can start the intent like below
startActivity(new Intent(android.action.VIEW, "http://m.me/{#user_id}"));