"Collection" feels very IA'ey, so I wouldn't use that. Try something more human. What do people use to refer to groups of people?
Try seeing if you find anything inspiring in various lists of synonyms. Here are some fun ones:
Some of those may feel like they belong in a videogame, but that's not necessarily exclusive - your app or site can have a lighthearted style too if it wants.
You could also try a list, although I don't like that one because it refers to the shape of the information. Conversely, Google+ opted to use circles because it evokes a certain shape, so there's that.
If this is a major feature, you might consider naming it something initially counterintuitive but brandable. Circles is a big part of Google+ so perhaps that line of thinking could work for you.
Try thinking about the nature of this group. Is it an arbitrary group? Or are they related to some other data somehow? For instance, followers on many social networks is a great name because it describes the purpose of the collection. See if you can find something similar for your group.