  In this work, we investigate the structure and evolution of a peer-to-peer
(P2P) payment application. A unique aspect of the network under consideration
is that the edges among nodes represent financial transactions among
individuals who shared an offline social interaction. Our dataset comes from
Venmo, the most popular P2P mobile payment service. We present a series of
static and dynamic measurements that summarize the key aspects of any social
network, namely the degree distribution, density and connectivity. We find that
the degree distributions do not follow a power-law distribution, confirming
previous studies that real-world social networks are rarely scale-free. The
giant component of Venmo is eventually composed of 99.9% of all nodes, and its
clustering coefficient reaches 0.2. Last, we examine the "topological" version
of the small-world hypothesis and find that Venmo users are separated by a mean
of 5.9 steps and a median of 6 steps.
