Online pro-health social networks facilitating smoking cessation through web-assisted interventions have flourished in the past decade. In order to properly evaluate and increase the impact of this form of treatment on society, one needs to understand and be able to quantify its reach, as defined within the widely adopted RE-AIM framework. In the online communication context, user engagement is an integral component of reach. This paper quantitatively studies the effect of engagement on the users of the Alt.Support.Stop-Smoking forum that served the needs of an online smoking cessation community for more than 10 years. The paper then demonstrates how online service evaluation and planning by social network analysts can be applied towards strategic interventions targeting increased user engagement in online health forums. To this end, the challenges and opportunities are identified in the development of thread recommendation systems for effective and efficient spread of healthy behaviors, in particular smoking cessation.