I think it is too hard to find where to post a possible hacker. Could you guys maybe make another section in the Runescape support for this? I think all of us legit players are trying to keep Runescape hack-free because getting hacked is annoying in every way. If posting more suspicious cases, we could collaborate and get rid of them so that our community does not get discouraged to play after getting hacked.
I think in most cases players do expose their login details by themselves on a phishing website or sharing their account with someone else who then uses his footprint on the account to recover it. So using the security advises and tools RuneScape does offer should solve most of the "hacker" problems. A great step by step guide how to secure your computer and account can be found here: https://support.runescape.com/hc/en-gb/articles/207498275-Securing-your-computer-and-account
If you recently got "hacked" feel free to send an email to firstname.lastname@example.org to let Jagex investigate the situation and let take them action if needed. Please note, that Jagex is unable to reply directly to your email.