I have the exact same problem with potted hibiscus with few leaves or the look like poodles with leaves on the tips and leaves here and there throughout.

Stop fertilizing them.
Just water them well, and mist.
You will see more leaves.

I have the same problem with all the leaves at the end of the stems. Leaves seem to yellow and drop very easily. Can a hibiscus be pruned back to encourage more bushy growth?

Tropical hibiscus only flower on new growth, jane tropicalgrower is absolutely correct. Prune back to encourage new growth. One way to do this is select one or two branches and cut back. In about 6 weeks, pick a few more branches and prune back. In this way, you'll stagger the pruning so the bush doesn't have that flattop look. However, if this seems like too much work, than just cut back all branches, but be prepared for the flowers to be delayed, until the new growth matures.