Gas giant
The smallest known extrasolar planet that is likely a "gas planet" is Kepler-138d, which has the same mass as Earth but is 60% larger and therefore has a density that indicates a thick gas envelope.
HD 102117 b
HD 102117 b is a planet that orbits the star HD 102117. The planet is a small gas giant a fifth the size of Jupiter. It orbits very close to its star, but not in a "torch orbit" like the famous 51 Pegasi b. It is one of the smallest extrasolar planets discovered so far.