Your site/site’s visitors are very active.
How is correct to write: your site visitors or your site’s visitors?
Keep the possessive, it's required.
When the your is absent and you are using it as a noun phrase, site visitors would be fine, but not with the your. Remember, your modifies site, not visitors here (by default).
In case you have defined earlier the expression 'site visitors' as a contextual noun phrase, then your site visitors will be valid, though with a different meaning.