Yes, you must advertise on MyCareersFuture if you intend to hire an EP or S Pass holder.
Advertising on MyCareersFuture will help you extend your outreach to more job seekers, and may enable you to identify a suitable Singaporean candidate as you had originally intended.
Regardless of the circumstances for hiring an EP or S Pass holder, you must advertise on MyCareersFuture for at least 28 days (4 weeks) before you submit an EP or S Pass application.