The only people that can find you on Catalyst are others within your organization that have also completed a Catalyst assessment and that have not opted out of sharing (it's on by default).
If you opt out of sharing, no one will be able to see you or your DiSC information, but you won't be able to see any of your coworkers either. The comparison tool within the "Your colleagues" section is a powerful tool for improving your working relationships and we highly recommend that you keep it turned on.
Note that your information will always be visible to your Catalyst™ administrators, no matter what the setting.