A person who steals people's friends for no apparent reason. Usually this happens when the friend digger has no friends herself, or when her close circle of friends are experimenting with different things. She will turn to a younger audience of people, and steal primarily from a sibling or close friend. Some people are dragged in through trickery that the friend digger uses.
Becca is such a friend digger, she always has to go and steal people's friends because she doesn't have any of her own.