We report follow-up observations of three poorly studied AM CVn-type binaries: CRTS CSS150211 J091017-200813, NSV 1440, and SDSS J183131.63+420220.2. Analysing time-series photometry obtained with a range of ground-based facilities as well as with the Transiting Exoplanet Survey Satellite (TESS), we determine the superhump period of CRTS J0910-2008 as $\rm{P_{sh}}=29.700\pm 0.004$ min and the orbital period of NSV 1440 as $\rm{P_{orb}}=36.56\pm 0.03$ min. We also confirm a photometric period of $P=23.026\pm 0.097$ min in SDSS J1831+4202, which is most likely the superhump period. We also report the first optical spectroscopy of CRTS J0910-2008 and NSV 1440 which unambiguously confirms both as AM CVn systems. We briefly discuss the distribution in the Hertzsprung-Russell diagram of the currently known sample of 63 AM CVn stars with known periods and Gaia data.