I don't recall seeing earthworms in sandy soil. They like rich organic matter such as broken down leaves.

"? A friend has suggested that the soil here is so sandy and so lacking in clay that it doesn't get compacted"

actually, the native soil on most of the coast is clay
there is a lot of river sand on top of it, depending on the area.

soil is VERY area dependent.
it can be completely different 100 yards away.

i pulled up the St Aug grass in part of my yard, added used coffee grounds, leaves and grass cuttings for 2 years
and my soil went from a thin layer of river sand on top of hard clay, to, **beautiful** soil...
(tons of worms now)
under 2 yrs.

Keep letting leaf litter, compost, and other decaying organic matter accumulate in your soil. And they will come. You may need to introduce a few. But they are quick little devils and there are surely some nearby and they will find it.

there are 2 general types of worms... compost worms, and earthworms...

you probably have some earthworms, maybe not many, but some...

if you want compost worms, you will have to add them, and keep feeding them, as are very different from earthworms.

compost worms LOVE coffee grounds... leaves also... lots and lots of leaves and grounds.. also fruit peels cardboard, newspaper etc... you will need to keep a thick mulch on top, so they can come up to feed without seeing sunlight.

i would start a worm farm and buy compost worms... when they start to multiply, in just a few weeks, you can take 1/3 of them and put in the garden.

I'm just a bit north of you in Myrtle Beach. I have lots of worms in my sandy soil, but the beds were all heavily amended by a previous owner, and I've kept up the mulching from all the pine needles that drop on my roof, car, driveway, lawn, patio... There are definitely more worms in the amended, mulched beds than in the lawn which has been given little attention. One advantage of this beachy sandy soil, is that my earthworms don't drown in a deluge. Up in Raleigh, NC, they would commit suicide on the driveway every time it rained.