Backyard birds come and go for various reasons. It's one of the mysteries of gardening with critters. Sometimes they have found another plentiful food source nearby and are feeding there daily. Sometimes it is because of predators in the area (when my wintering red-shouldered hawks move into my oaks, the birds lay low for weeks). Sometimes it's because the birds have moved on. Goldfinches are only passing through, so perhaps your flock has moved on for now.

In the spring, backyard birds often disappear while rearing their young. They try to be inconspicuous as to where they are nesting and where the vulnerable chicks are, and they often rely heavily on insects for the protein necessary to raise healthy babies. Even seed-eaters like cardinals will start bulking up their diets with insects, and as a result, might not come to the feeder as often.

And then, sometimes you can figure out no rhyme or reason for them to disappear, but they will almost always come back in a few days to a few weeks, depending on why the left. Hang in there. Keep the feeder stocked with fresh seed, and plenty of water in the birdbaths, and you will see them back again before too long.

Good luck!
Marcia