OK, so I search for people in Steam and don't receive any results.
This is probably something really simple, I have looked it up on Google, and there are solutions such as the difference between usernames & show names. I tried searching for myoelectric [youtube gameplay commentator] using his Steam details from his channel; this doesn't show any results either. -LoXodonte1.
As you said, there are differences between usernames (SteamIDs) and shownames (Display Names). "myoelectric" most likely has his SteamID on his channel, which does not show up when searching. To add someone via their SteamID, open the "Friends window, and click "+ADD A FRIEND". Then type in the SteamID.