On the right-hand side of every members page, there is a column that you should be able to leave public message. Leave a message there requesting that the member add you as a friend OR AS mr_blue suggested, send a "Friendship Request". That is also located on the right-hand side of a member's page for those members who will only accept messages from their friends. The [Send Friendship Request] is directly above the [Add this member to your friends] option.