Industry 4.0, as the fourth industrial revolution, represents significant challenges and numerous innovation opportunities for future product realization. A critical area of Industry 4.0 is the advancement of new design theories, design methods, and design principles to drive and enable the revolution with designers, engineers, teams, and organizations. This paper focuses on the advancement of a design theory and design principles for a growing manufacturing capability for Industry 4.0: additive manufacturing (AM). With high degrees of freedom, the field and use of AM requires design guidance and highly practical knowledge for supporting ideation processes, enabling understanding of capabilities, and creating a basis to innovative with the technology. Some design principles for AM exist in the literature; however, designers seek more fundamental and practical design guidelines for successfully creating and building their customized design artefacts, especially as Industry 4.0 moves forward. In this study, a crowdsourced repository for additively manufacturable components is used as the source of design data, within an empirical study, to extract practical design principles for AM. A total of 23 crowdsourced design principles for AM are extracted and clustered according to level specificity: (i) design for manufacturing, (ii) design for digital manufacturing, (iii) design for AM, and (iv) design for fused deposition modeling. These 23 AM design principles, as a foundation for AM design and Industry 4.0, are provided in a common framework; expressed for ready use by designers, developers, and researchers; and illustrated through some contemporary designs.