What would be a polite way to say "eyeballs"?
Solution 1:
Sometimes the word visitor is overly generic, but sometimes that term gets customarily used nonetheless.
What would you call someone who visits a museum, or a zoo? Not everyone who visits a planetarium is an astronomer. You might call them a guest, or a patron, or a customer – or you might decide visitor is about as specific as you can get.
As for websites, I would think browser might be an apt term, except that word is already used to refer to the software that allows the user to visit the website.
The best term I can think of is user. It may be a bland term, but it's the word software developers customarily employ when referring to the individual who is typing at the keyboard, and clicking with the mouse.
Solution 2:
"Surfers" is possible, although perhaps a little archaic now.
In web advertising they talk about "impressions" to mean distinct accesses to a piece of content. That may be the word you're looking for.
Solution 3:
The term Targeted Visitor is used in a wikipedia article about revenue models for online advertising. The article also defines terms impressions, loads, views, clicks, actions, acquisitions, leads, sales, and conversions in this context, with each term representing a different website statistic, or in a few cases a different name for the same statistic. Webopedia defines terms click-through, ad clicks, requests, and click rate.
Solution 4:
People who are actively involved to the point that they even create content (you mention write) are indeed not merely visitors. Being active, they are participants. If people must join to fully participate then you can call participants members.
(There is the word subscribers but, with respect to a website, that really should refer to people who subscribe to RSS/Atom feeds, not to people who create accounts, otherwise it is confusing. Feed subscribers are basically trying to minimize interacting with your website by getting it in digested form and will turn into participants sometimes when an item of interest trickles into their reader.)
From participant there are various leads if you look in a thesaurus: http://thesaurus.com/browse/participant