  Nowadays online social networks are used extensively for personal and
commercial purposes. This widespread popularity makes them an ideal platform
for advertisements. Social media can be used for both direct and word-of-mouth
(WoM) marketing. Although WoM marketing is considered more effective and it
requires less advertisement cost, it is currently being under-utilized. To do
WoM marketing, we need to identify a set of people who can use their
authoritative position in social network to promote a given product. In this
paper, we show how to do WoM marketing in Facebook group, which is a question
answer type of social network. We also present concept of reinforced WoM
marketing, where multiple authorities can together promote a product to
increase the effectiveness of marketing. We perform our experiments on Facebook
group dataset consisting of 0.3 million messages and 10 million user reactions.
