N00b's correct.

In short, your group seems to be entirely dedicated to recruiting by just telling people to join your group, and since no effort seems to be spent at doing whatever is the group's purpose to do, nobody will join since they do not see which purpose it is. Instead of going around recruiting people all the time, try doing something useful so that people know that there is actually any reason for joining. It might get you more members than just going around namedropping "PE" at every opportunity.