You can use the 
list of submissions and the filter options to easily access this information.
Please go to:
Overview => Submissions & Reviews => List of Submissions... select "
Show more filter options" and set the "
Special Filter". 
Here you can choose from many filtering options (see image).
You can also have a look at the reviews received on this page:
Overview => Submissions & Reviews => Results of the Reviewing Procedure & Decision About AcceptanceYou can find the same filter options there.
Furthermore, you can sort by the column "Reviews" to get a quick overview.
See also:
Evaluating the Review Results and Setting the Acceptance Status of SubmissionsNB: 
We recommend assigning at least 3 reviewers to each paper, as unfortunately some reviewers forget to submit their reviews. 
You will then have at least 2 reviews for most papers.