User Referrals 
vBulletin includes a feature that will allow your community members to be rewarded for recruiting new users to your bulletin board. A user can gain a referral by attracting a new user to the vBulletin forum via a special referral link. A typical referral link looks a bit like this:

http://www.yourwebsite.com/vbulletindirectory/m/forum/index.php?referrerid=$userid

(Where $userid is the unique ID number of the user)
Note:
Your users can find out their specific referal URL by visiting your vBulletin board FAQ page (by clicking on the button at the top of the page). Once a user has found out their unique URL, they can then pass the URL on to their friends and colleagues. If any of these visitors register for an account on your bulletin board via this special link, the user will earn one referral.
In addition, a Referrer field will be included on the initial user registration screen that will allow visitors to grant a referral point to an existing user even if they haven't visited the bulletin board via the specially coded URL.
Note:
Before the vBulletin software will begin to track referalls, please make sure that the "Referrer - Enable the referrer system?" setting is turned on in the vBulletin control panel "options" screen.The administrator of the vBulletin software can use the "Referrals" control panel feature to find out which users have received referrals. In addition, the administrator can view a list of all the new usernames that the user has referred to the bulletin board. Once the administrator clicks on the "Referrals" link (under the "Users" section), the following form will appear on the right hand side of the screen:

This form will allow you to return a list of all users who have earned referral points during the time period you define using the two form fields - the results form will also detail the number of points earned by each user.
User Contributed Notes: User Referrals Add a Comment