In general, the effectiveness of promotion and communication flows along the same lines as any type of communication. It is most effective when it is most personal; it is least effective when it is least personal.
The most effective promotion and medication is a personal invitation delivered in person face-to-face. It is most effective in a one-on-one setting. But it can also be effective if one missions advocate or missions team member is making an appeal to a small group or Sunday school class. Effectiveness diminishes as the audience grows.
Effectiveness of communication also has a relational component. The youth group will be most effectively reached by someone they recognize and relate to. That might be the youth pastor or it could be a respected member of the youth group. Similarly a well-known leader or participant in the ladies Bible study is the best person to promote a missions event or communicate missions information to the ladies Bible study.
Personal communication delivered through a less personal vehicle can be moderately effective. Phone calls, email, social media postings on the Internet, hand written notes or invitations, etc. all fall into this category.
Less personal communication includes flyers, bulletin inserts, handouts, bulk mailings, group emails, etc.
The least personal communication and promotion are passive instruments, like posters, bulletin boards, general public address announcements, etc.