Health communication campaigns have been used to promote healthy behavior change in a variety of health domains around the world. One element of formative research to develop these campaigns is selecting the topic or topics to be addressed in the campaign, called themes, or groups of beliefs. Extant approaches to theme selection consider each theme individually, and do not consider the relationship among themes, nor the influence of spreading activation processes, in which exposure to messages about one theme may have effects that spill over to related, but non-targeted themes. This dissertation seeks to contribute to understanding of these issues in the context of anti-tobacco cigarette smoking behavior among U.S. young adults aged 18 to 25 years who have smoked less than 100 cigarettes in their lifetimes. Study 1 is a secondary analysis of existing survey data, demonstrating that themes can be promising yet can vary with regard to their inter-correlation. Studies 2 and 3 validated messages using an online survey experiment to ensure that message exposure led to increased targeted theme endorsement. Results from Study 3 suggest broader spreading activation processes, such that those exposed to anti-smoking and pro-recycling messages demonstrated stronger theme endorsement, even for non-targeted themes. Study 4 compared the effects of exposure to one promising theme, two promising themes, and two highly correlated and two uncorrelated themes. Among those who passed the attention check, intention not to use tobacco cigarettes was stronger among those exposed to any message, including those about recycling, relative to those in the no message control group. Targeted theme endorsement was higher when participants were exposed to messages targeting a particular theme, regardless of whether they saw messages about one theme or two. Results support broader spreading activation processes, such that those exposed to any anti-smoking message reported stronger support across all anti-smoking themes. Evidence from these studies suggests that effects may be similar when focusing on one theme or dividing exposures among two promising themes, regardless of their correlation with one another. Campaign planners should consider that exposure to persuasive campaign messaging may have broader effects beyond message-targeted themes.