Can You Search Reddit by Username?

Yes, but only with the exact username. Reddit has no partial or fuzzy matching, so a near miss returns nothing at all. Capitalisation is ignored, and you can use the bare name, a u/ handle, or a full profile URL.

What a username search gives you

Going straight to reddit.com/user/name confirms the account exists and shows its karma, creation date and recent public activity. Reddit's search box also accepts author:username, which returns that account's posts, though never its comments.

Where it stops

• No partial matching. If you remember roughly what the name looked like, there is no way to search for it.
• The author operator misses comments. Reddit does not index comment text, so comments have to be browsed from the profile instead.
• An empty result is ambiguous. A name that never existed, a deleted account, a suspension and a shadowban all look identical from outside.

If a name returns nothing, checking the username narrows down which of those four states you are looking at.