More ways small churches can serve their communities
Small churches can adopt the same (or different) unengaged, unreached people groups currently living in the United States.
In addition to overseas work, consider how you can share the gospel effectively and long-term with a people group in America. States like Oklahoma, Louisiana, North Carolina, and Iowa, to name only a few, have thousands of people who comprise various unengaged, unreached people groups.
They are as spiritually destitute and lost as those living overseas without a gospel witness. If your church is geographically near one of these groups, then begin praying about how you can begin a ministry to them. Preach on the value of avoiding worldly wealth and, instead, storing up treasures in heaven in hopes that some of your members will envision themselves selling their homes and moving closer to this group to encounter them daily in their neighborhoods.
These groups, depending on location, are either centralized (think one main neighborhood) or decentralized (think ethnic neighborhood[s] spread throughout a city). But as a people group, they share common languages and customs. Interacting with them in their environment, learning their culture, understanding their traditions and religion(s) will allow you to be better prepared to engage them with the gospel.
Befriend them. See them not as a project to be conquered or a task to be checked off the list, but people who are lovable and need to learn about their Creator.
Churches that are willing to pursue both international and national unengaged, unreached people groups could look, for instance, at the Khuen people. There are 3,000 in the San Francisco area and 13,000 in Myanmar (formerly Burma). Churches in or near the Bay Area could interact with U.S. residents first ...