You'll probably get the quickest answer to your question by posting here on Splunk Answers. To easily ask a question about an app, go to the app's page on Splunkbase and click the "Ask a Question" button, which will link you to the Splunk Answers new-question page, with the app's "Answers Tag" (e.g. app-windows-splunk or app-runsavedsearch-lowell) already populated.
The rest of the apps on Splunkbase are supported by the community. Usually this means that whoever uploaded the app will be most active in answering questions about it, although sometimes fast-moving community members will jump in and answer questions too.
Of course, if you're using a community app, and you understand the app, but are having a general Splunk problem, feel free to use all the normal Splunk channels: chat, tickets, answers, etc., just be sure to focus on the Splunk issue.