  Guiding users to actively expanding their online social circles is one of the
primary strategies for enhancing user participation and growing online social
networks. In this paper, we study the active friending problem which aims at
providing users with the strategy for methodically sending invitations to
successfully build a friendship with target users. We consider the prominent
linear threshold model for the friending process and formulate the active
friending problem as an optimization problem. The key observation is the
relationship between the active friending problem and the minimum subset cover
problem, based on which we present the first randomized algorithm with a
data-independent approximation ratio and a controllable success probability for
general graphs. The performance of the proposed algorithm is theoretically
analyzed and supported by encouraging simulation results done on extensive
datasets.
