People use Twitter to communicate with companies and friends, and ask for or share information. Here, we explore participation and engagement in an information-gathering 'social crowd'. We first present a study of engagement behavior through both Twitter Ads and direct outreach, and find that direct outreach achieves a higher engagement rate. Second, by showing people other users' participation with a shared interest, we explore the potential for engagement of social crowds. We demonstrate the benefit to engagement of sharing social context, present a preliminary step towards deeper studies on the social component of engagement, and suggest directions for understanding and supporting social crowd engagement.