Welcome to Steemit/Dtube!
If you know their usernames, you can type it into the actual menu bar. Check out the screenshot below to see what I mean. If I was looking for a particular user, I would just delete coruscate and put in their user name instead.
We are definitely still in beta testing! So sometimes things aren’t the most intuitive.
Ahh thanks you! I just figured out how to respond to comments lol , so to do it this way you need to get the spelling of their channel exactly it's not like a search function yet. Thats ok, I'll make due. Hopefully a searchy type function for channels will come in time :)