Survey concerning peer-reviewing

Public health journals are encountering serious problems to find suitable reviewers for articles in a reasonable time with a reasonable number of invitations. This slows down the peer review process, increases the workload for editors, and floods scientists with invitations. IJPH and PHR would like to increase the efficacy of their pre-publication peer review process. How can we promote the willingness of scientists to review? What is your perspective and what do you recommend to overcome the peer review crisis?