The most impactful social media platforms you may like to consider:
Instagram - steady and used by most casting directors and filmmakers. It's an easy platform to maintain without having to do videos, which suits the boomer and millennial age bracket of those most often hiring actors. Great visibility due to photos and videos being primary media used.
Twitter - Political and social commentary. A good platform for social growth, but not as important to visibility as instagram.
Tik Tok - great for building an audience fast. Strong Gen Z / Y user base but others do use it also.
Facebook Fan Page - Grab the handle to save it, but you really don't need one of these until you have some level of notoriety.