Word of mouth. People love to say nice things about people they know, but only if it's a sure thing. If you occasionally do the wrong thing or upset people in inappropriate ways, they won't say anything. There's a wide swath of I like this person but won't bring up his/her name to others for X or Y reason.
People will bring up your name in positive situations, which leads to new connections to you without effort on your part.
People will bring up your name in positive situations, which leads to new connections to you without effort on your part.