Currently, only a full-site publish triggers reindexing the site. It may be impractical though to publish the whole site each time collection items are updated via API (such as products, blog posts etc.), as it could publish some work-in-progress. However, until a full-site publish, new items cannot be found on the site using the search feature.
It would be useful to have some control over this, either through some parameter, or via a dedicated API call to re-index.