The main reason may be because your accounts are still indexing.
Check the indexation status of your accounts. While the account is indexing we can't view all search results because we need some time to process your content and build the search index for you.
When you see 100% beside your accounts you can search!
If you still can't find what you are looking for make sure you have added all the necessary accounts.
One more tip: Try to change your search query by using our suggestions.
If you have any further problems with search please contact us firstname.lastname@example.org