Most research in massive online youth communities has focused on understanding patterns of participation and collaboration in games, social networks, and virtual worlds. Few studies have examined the nature and dynamics in amateur design communities where youth contribute content they have designed themselves. In this paper, we examine quantitative trends of participation in a youth design site focused on programming. Scratch is an online community with over 1 million registered youth designers 11-18 years of age. Drawing on a random sample of 5,000 youth programmers and their activities over three months in early 2012, we examined log files that captured the frequency of their contributions and comments on the site, making visible distinct classes of users who engaged in different sets of practices that support design on a collective scale. In the discussion we discuss implications for the design of collaborative spaces, tools, and communities.