With the recent hype concerning three-dimensional (3D) printing technology, affordable 3D printers have been launched, enabling individual machine owners to download or create design files and thus produce artifacts. As a design community, Shapeways—which comprises over 300,000 members and 25,000 online shops—commercializes and promotes good ideas using 3D printing technology (Shapeways, 2015). Through Thingiverse, people can globally upload and share design modeling files without cost and print out items as desired. In general, 3D printing communities provide data without charges and witness gradually increasing data sharing rates. Literature on 3D printing mainly focuses on cases of technology-related patents, policies, and intellectual property rights. Thus, there is a paucity of empirical studies on 3D printing users. To overcome the limitations of previous studies, this study first builds on both social cognitive and social capital theories to elucidate the effects of 3D printing community users’ self-efficacy; altruistic tendency; and perceived structural, cognitive, and relational capital on their voluntary knowledge sharing and innovative behaviors. Second, it aims to verify inter-group differences in innovative behaviors of 3D printing community users while considering either high or low levels of fashion innovativeness and fashion involvement. For this verification, antecedents of knowledge sharing are elicited from previous research followed by an interview and a questionnaire survey with 3D printing community users to substantiate such antecedents. Next, the data collected from the interview and survey is analyzed using SPSS 18.0. The results indicate that first, altruistic tendencies influence knowledge sharing, which is consistent with the social cognitive theory, whereas structural, cognitive, and relational capitals affect knowledge sharing, which parallels social capital theory. Second, knowledge sharing in 3D printing virtual communities exerts significant effects on innovative behaviors. This study establishes the antecedents and consequences of knowledge sharing in 3D printing virtual communities and proposes a model for effective knowledge sharing, which is projected to stimulate the application of 3D printing technology in creating and sharing fashion design content and providing substantive data for market formation.