To add sims you'd like to share information on to your profile, start by editing it:
Then click on the My Sims tab to see the following screen. You can add any kind of sim information you would like, including their avatar. They can be any kind of sim - humans, supernaturals, pets, and even small animals.
When you are done filling in information on a sim, be sure to click the "Update" button near the bottom.
You can add as many of them as you like - simply click on the "+ Add Sim" button and a new blank form will be added for you to fill in for another new sim.