We do not current have a feature to add individuals to your page as "co actors". IMDb and IMDbPro both have tools you can use to achieve this in a different way though.
For IMDb, you can use the List feature to keep track of individuals you have worked with by simply creating a list of their pages. Frequently asked questions regarding our list feature can be found here.
A member benefit of IMDbPro is our "Shared Credits" widget. This widget allows you to view the credits you've shared with an individual (and others in the same projects) when navigating to their page. The many member benefits of an IMDbPro membership are detailed here.