User-generated contents (hereafter, UGC) are the contents produced by individual users. In addition to the conventional role of individuals as consumers, nowadays individuals can play an additional role as producers. Individual producers create their own virtual contents and share them with others, and some active producers try to communicate with their UGC users. As information technology advances and diffuses over space and time, this UGC-related market has grown substantially with the growing numbers of participants and the high quality contents. The popular UGC platform sites include: Youtube.com, Twitter.com, Facebook.com, and Wikipedia.com, which in fact belong to the top 10 Internet sites according to site traffic(Alexa Internet Inc., 2012). There has been much effort to understand the mechanism by which online performance is determined. Well-studied measures include product sales(Van den Bulte and Joshi, 2007;Dellarocas et al., 2007), sales ranks(Chevalier and Mayzlin, 2006), company profit(Liu, 2006;Chan et al., 2011). Key factors to derive online performance include product quality(Dichter,1966), word-of-mouth among consumers(Liu, 2006), producers’ particiation(Schwartz et al.,2011). For example, it is well known that product popularity has a positive influence on product sales(Kohler et al., 2011). Here, product popularity serves as a proxy for product quality and performance is measured using consumers’ choices. UGC platformsites provide users opportunities to not only select but also engage by reviewing products and making recommendations, and this kind of behavior can reflect consumers’ engagement(O’Hern et al., 2011; Schmitt et al.,2011). Thus, this research extends performance measures beyond choice-based ones and incorporate consumers’ engagement-based measure. On the UGC platform sites, producers can easily observe communication among users, and some producers participate in consumers’ conversation(O’Hern et al., 2011). Despite this growing producers’ participation, there is limited research on its effect on performance. On the one hand, producers’ communication with users can improve the relationship with users, which in turn increases users’ interest and promote product choice(Doney and Cannon, 1997). On the other hand, producers’ participation can inhibit consumers from speaking out(Kohler et al.,2011). Therefore it is needed to understand whether producers’ participation improves or deteriorates UGC performance. This research collects data from Youtube.com in the category of ‘how to & style’ using snowball sampling. On Youtube.com, users can view videos and leave comments, and also upload video clips. All the video-related and users’ activities are collected and analyzed. The empirical analyses support all the proposed hypotheses. First, producers’ participation has the positive impact on the choice-based performance and this positive effect strengthens with increasing product popularity. This means that when producers of popular products communicate with consumers, the choice-based performance improves(Kohler et al., 2011). On the contrary,producers’ participation has the negative impact on the engagement-based performance and this negative effect gets stronger as products become more popular. This means that when producers of popular products participate in consumers’ conversation, consumers are demotivated and do not express their opinion(Dellarocas et al., 2010). Producers’ particition has the positive effect on consumer choice but the negative effect on consumer engagement. Therefore, in order to understand to what extent producers participate, both performance measures must be considered simultaneously. Further empirical investigation provides the following practical guidelines to decide on the level of producers’ participation. First, producers of popular UGC should activily communicate with users. Avid participation by producers of popular UGC increases consumers’ choices to the much greater degree than it reduces consumers’ engagement, and collectively improves the aggregate performance. Second, producers of mediocre UGC should make discreet decisions and decisions should be based on the way that multiple performance measures are aggregated. Third, producers of unpopular UGC should pay more attention to UGC themselves and try to improve UGC quality.