Clarivate recently added a new database to the Web of Science interface. The Preprint Citation Index helps you find articles that haven’t been formally published yet but are available on preprint servers and see who has been citing them already.
A direct link to the Preprint Citation Index can now be found on the A-Z databases page on the “O-P” tab. For more info from Clarivate about this new database, see this February 3 announcement.