We describe a new species of arboreal microhylid frog, genus Platypelis, from northeastern Madagascar and report the expansion of distribution ranges of two other species. Platypelis laetus sp. nov. is small to medium-sized (24.3-25.6 mm snout-vent length) compared to other Platypelis, exhibits a greenish colored throat and was found in bamboo forest of the Sorata Massif. Its advertisement call consists of a single short tonal note repeated at regular intervals in long call series. Based on DNA sequences of a fragment of the mitochondrial 16S rRNA gene, the new species was placed in a clade with Platypelis olgae from the Tsaratanana Massif, and with two other, unconfirmed candidate species from the Sorata Massif and from Andravory, herein named Platypelis sp. Ca12 and Ca13. Molecular divergences among these lineages were substantial, amounting to 7.6-8.1% uncorrected 16S p-distance to the closest nominal species, P. olgae, from which the new species is also distinguished by a lack of allele sharing in the nuclear RAG-1 gene. We also provide new records of Platypelis alticola and P. tsaratananaensis from the Sorata Massif, supported by molecular analysis. This confirms a wider distribution of these two species that previously were considered to be endemic to the Tsaratanana Massif. However, their populations in Sorata were characterized by a certain degree of genetic differentiation from Tsaratanana populations suggesting they require more detailed taxonomic assessment.