You should be able to find any user in Spotify using Search, but sometimes this workaround can be helpful.
If you can’t find another user just by typing their name, it’s likely because they don’t have a display name. If you know their username, try searching spotify:user: followed by their Spotify username instead (with no spaces).
If you connect your Spotify account to Facebook, you can view a recommended list of friends and featured people to follow. For more info on how to do this, check out this article.