I've seen this question pop up a few times already, so figured I should create a post to talk over the sparse search results following the migration.
When there is a major migration of content (like the one that took place with the cloud migration last night) the search index for the site needs to rebuild to recognize and categorize all of the content that has been moved. This process can take a few days, and as a result, search results from within the search bar, within content pages, and when searching to create a stream may be impacted for the next few days. Search should improve every day as more content is indexed, and should be completely back to normal in the next few days.