You need to be logged in with your credentials to be able to see available influencers. Once you do so, you can click on “Find” on the left-side toolbar. This will bring up the search page. There, you can select “Influencers” and then refine your search request by adding more search criteria and/or filters. On the right-side panel choose the campaign you are going to add influencers to.

You can also expand search options under Show all filters button.