Mu Koh Hong, the islands of Koh Hong, are located in Than Bok Khorani National Park in Krabi Province. It is a collection of large and small islands like Koh Lao (or Koh Sa Ga), Koh Lao Riam, Koh Pak Ka and Koh Lao Lading. In general, the excursions offered by the local agencies take you to Koh Hong and at least to Koh Lao Lading and Koh Pak Bia for a day or half day tour. It is a nice tour but also very popular and therefore if you can manage to have few people on one of the islands by leaving early in the morning or visiting it around 4 p.m., there will be a lot of tourists on the others islands especially in high season (December to end of March ).
To go visit Koh Hong, you can also book one of the tours above.