Roblox reports do work. I sent them an email one time about a person breaking the rules, (their email is
info@roblox.com) and some of the words said:
"We want everyone to enjoy their experience on Roblox. We have moderators online around the clock reviewing reports and helping to keep Roblox fun and safe for all players. Remember, even though you cannot see if an account is moderated, our team does take action against accounts caught violating the Terms of Use and Community Rules.
Moreover, we understand that you might feel that nothing has been done. However, that's not the case. Once you use the 'Report Abuse' option a ticket is generate and may take a few minutes to reach one of our live moderation agents. ROBLOX moderators are a team of employees who work diligently around the clock to review and apply appropriate consequences when necessary."
Furthermore, it may take some time for them to check the reports to make sure that they are accurate. They need to check the chat log, and other things to insure the reports are true. When you report someone, it does not mean that they will be banned automatically.
Thousands of roblox reports are sent everyday and even more are false reports just to get a user banned.