$addUsersToThread
Add users to a thread
Usage
$addUsersToThread[Thread ID;User 1 ID;User 2 ID;User 3 ID....]
Example (Add the triggerer to a thread):
$addUsersToThread[1024373454578917426;$authorID]
Example (add multiple users):
$addUsersToThread[1024373454578917426;$authorID;788361834360864808]