This is a different exchange that seems to conclude that there is no good single word. Some suggest Member.
https://ux.stackexchange.com/questions/95088/whats-a-good-single-word-term-that-means-a-user-whos-signed-in-to-your-websit
Other possibilities:
If you are looking for a word to describe recent (but not necessarily current) users I'd suggest returner as it implies that they are likely to be back. (This is how I think of active users. They generally interact with the product, but might not be currently on). Also, constituent might work depending on your context. Constituent is normally used for a voter in an election, but does imply occasional interaction and is most likely not used for anything else on your application.
For specifically people who are logged on at this moment in time I might suggest submitter. However, this would seem to also include anyone that has submitted a request even if they have now logged off (for example a bug report might have a submitter that is not current). Another option is actor. Actors are be definition doing some action (outside of movie/play context) and therefore is a decent word for the currently active users.
If you just want unique words that are marginally related, what about bustler or hustler. They both share the same formal definition according to Webster, but the second has a bad connotation so the first is a better option. Both imply activity which is related to currently logged on. You could even use a more out there word such as adventurer and just have a local comment giving it meaning.
Overall, I believe Constituent and Actor are the best two options I could come up with.