Hi! There are many orgs to volunteer but it depends what your passion is and what you want to do. There are homeless shelters, animal shelters, mentoring for kids and much more. here is a good site with lots of ideas:
Myrtle Beach Volunteer Opportunities
I volunteer with
WARM if you want to help animals, it's a no kill shelter. Also help
Street Reach - Home on occasion, even if it's just going to Costco and buying supplies, they need them. This is another I've been wanting to get to but haven't been able to so maybe you would be interested:
Myrtle Beach Haven - Home
Thats really great you want to help and I'm sure any org you go to will greatly appreciate it!