Once the Investor Link Module has been activated users will see a Linked Investors table within the investors “contacts” tab.

To Link new investors click "+ Link Investor"

Choose the active Investor profile from the drop down and define the relationship.

This is only a 'one way' connection though, and if users wanted both investors to ‘see’ each others profile, they would have to connect both profiles VIA the Linked Investors table. Also, each linked profile must have an active investor portal in order for the other investors to view their portal successfully.