  Friending recommendation has successfully contributed to the explosive growth
of on-line social networks. Most friending recommendation services today aim to
support passive friending, where a user passively selects friending targets
from the recommended candidates. In this paper, we advocate recommendation
support for active friending, where a user actively specifies a friending
target. To the best of our knowledge, a recommendation designed to provide
guidance for a user to systematically approach his friending target, has not
been explored in existing on-line social networking services. To maximize the
probability that the friending target would accept an invitation from the user,
we formulate a new optimization problem, namely, \emph{Acceptance Probability
Maximization (APM)}, and develop a polynomial time algorithm, called
\emph{Selective Invitation with Tree and In-Node Aggregation (SITINA)}, to find
the optimal solution. We implement an active friending service with SITINA in
Facebook to validate our idea. Our user study and experimental results manifest
that SITINA outperforms manual selection and the baseline approach in solution
quality efficiently.
