  The affiliation with various social groups can be a critical factor when it
comes to quality of life of each individual, making such groups an essential
element of every society. The group dynamics, longevity and effectiveness
strongly depend on group's ability to attract new members and keep them engaged
in group activities. It was shown that high heterogeneity of scientist's
engagement in conference activities of the specific scientific community
depends on the balance between the numbers of previous attendances and
non-attendances and is directly related to scientist's association with that
community. Here we show that the same holds for leisure groups of the Meetup
website and further quantify individual members' association with the group. We
examine how structure of personal social networks is evolving with the event
attendance. Our results show that member's increasing engagement in the group
activities is primarily associated with the strengthening of already existing
ties and increase in the bonding social capital. We also show that Meetup
social networks mostly grow trough big events, while small events contribute to
the groups cohesiveness.
