Is this the name of the file that I need to be editing:

jquery.tokeninput.js

Thanks. One last question about this topic -- if I do disable the autocomplete feature, will the admin still be able to send messages by security role but there will no longer be an autocomplete feature?

Are you sure the message center module only allows successful searches to be achieved if two users are friends or belong to the same social group? I read through the manual carefully and nothing seemed to indicate that. It appears that this setting can be achieved in the Member Directory Module where the manual notes, "The Member Director module can be configured to only display members of a particular role or relationship such as friends or members whose activities you are following."

I have been testing the message center module. I have no social groups on my site and no users are friends with other users. However, if I take a user account they can successfully search for any user account on my site in the message center module with the help of the autocomplete.