I've installed a new mod on the forum. This allows you to tag members on the forum. When they are tagged, their name will transform automatically into a link to their profile, and they will be alerted to this with a link back to the thread.
You can tag then using the UserName syntax, same as on Twitter / Facebook. Autocomplete is also supported, so you will see a list of usernames being populated as you type.
Full guide can be found here: Tag someone in a post