I am trying to search people by username but it keeps coming up search disabled? Am I doing something wrong (am relatively new to the whole 365 project!) or is there another way to do it?
That's not you. That is the web-site. Just do a regular search with the user name and you should find links to things they've posted or someone posted about them. If so that will get you where you are going.
If it's someone from your follower or friends lists, go to the list, click on control F on PC, or command F on a MAC and type in the name in the box that appears. For people already on your lists, this is more efficient anyway.
www.365project.org/****** **=username