As data becomes an integral part of our lives, the general public faces the increasing need to actively engage with data to participate in daily activities, support personal goals, and understand social issues. Formal data science training, however, remains out of reach for most people and does not cater to their diverse needs related to data. Emerging informal settings, such as online and in-person social spaces and community workshops, offer accessible platforms for diverse and meaningful data engagements. However, current research on data literacy does not fully capture the diverse ways that the public interacts with data in these informal environments. This dissertation presents four studies exploring the ways people interact with data in informal settings and examines the challenges and needs emerging from these engagements. These findings guide future research and shape the design of tools to foster data engagement in diverse informal environments. Study A illustrates a mixed-method analysis of 400 Scratch forum discussion threads and more than 240,000 user-generated projects, unpacking the benefits and drawbacks of interest-driven participation that involves data in a large online community. Study B presents a semi-structured interview study with 14 Kaggle users on their collaborative and communicative practices in working with large datasets, highlighting the needs and challenges in communicating procedures to a diverse audience and fostering collaboration among users of different experience levels. Study C contains a theory-driven quantitative analysis of a large collection of Twitter messages that involve discussions about COVID-19 vaccine data, identifying features that differentiate critical engagement with data from conspiracy discourses. Study D presents a constructionist system that scaffolds novices to programmatically analyze and visualize data, as well as the insights from user study workshops that showcase the diverse range of concepts, perspectives, and practices that the system can support. Together, these studies reveal a pluralism in people's competencies and epistemological pathways concerning data engagement--what I refer to as "data literacies"--that should be accounted for in the research and design of technologies for data literacies. This dissertation contributes rich empirical knowledge on the public's engagement with data in a range of informal settings, various design recommendations for informal environments to support data literacies, a call for acknowledging the pluralism in data literacies in the design of tools and interventions, and a sociotechnical framework for conceptualizing and designing to support data literacies in informal settings. [The dissertation citations contained here are published with the permission of ProQuest LLC. Further reproduction is prohibited without permission. Copies of dissertations may be obtained by Telephone (800) 1-800-521-0600. Web page: http://bibliotheek.ehb.be:2222/en-US/products/dissertations/individuals.shtml.]