Magma does not have a way for you to search up users by name. The search bar that you see in your Artdesk is only for searching drawings. But if you know a friend's username, it's easy to find their profile.
If you know their username...
First, the username is usually the blue text that follows the @ symbol.
In this example, Ryan | Magma is the displayname, but ryan-magma is the username.
To find your friend's profile, type https://magma.com/artist/[username] and replace [username] with their handle/username. Do not include the @ symbol.
So for the above example, the profile link would be https://magma/com/artist/ryan-magma
From their profile, you'll be able to follow them and their posts will appear in your Feed. See more about the Public Profile and Following in this guide.