BuddyPress Restrict Messages is a useful plugin for sites that wish to control in-site spam to users. It comes with two modes of operation – Admin control and User control, these allow users or site admin to restrict messaging to friends, followers or just to members of the same groups.
BuddyPress Follow allows members of a BuddyPress social network to follow each other, it places follow buttons on each members profile and in the members page and adds extra tab’s in each members profile page, one showing who is following you and the other showing who you are following.