Every social service aims to achieve massive growth and deep engagement. But if forced to choose just one of these attributes, I would pick engagement every time. An active user base implies product/user fit for a social service.
Aside from the core functionality of social services, which is a solved problem (profiles, messaging, feed), the essence of a social startup is culture - the values of the community, the mores, the manners of interaction. The right culture attracts users, encourages participation and drives growth.
For proof, look at Reddit’s growth to 2B page views and the clear values they promote for their community. The same is true for Pinterest. Did you know Pinterest has Pin Etiquette?
Successful online cultures replicate the behaviors of offline groups (from political groups to book clubs) which communicate a clear purpose for organizing members, defined norms for interacting, and effective tools for solving their members' needs and wants.
So how does a social service become massive? The key is focusing on culture to drive engagement at the very beginning. I’ve drawn my take on the path using this engagement/growth 2x2 matrix to describe the path from the Ghost Town to the Rave.
4 - The Ghost Town: low engagement, low growth Obviously, the most challenging (and most common) place to be, startup in this situation can focus either on fast growth (which would lead to the Leaky Bucket) or driving engagement (the Garden Party).
3 - The Leaky Bucket: low engagement, high growth The challenge with focusing on fast growth without engagement is that it doesn’t build or reinforce culture. Users are brand new and don’t know how to contribute to the community. Plus, it’s hard to understand what will improve the product when churning through large volumes of unengaged users.
2 - The Garden Party - High engagement, low growth The culture of the social service has been set, the product meets the needs of a small group of people and the party is “polite”. Now it’s time to garner more users while keeping the same values.
1 - The Rave: high engagement, high growth Lots of people have arrived, they know why they came and what the party is about so they’re having a great time.
I believe engagement is the foundation of growth. And because, culture cannot be tacked on, the engagement problem can’t be solved through growth alone. Instead, culture has to be inculcated into a community over time.