  It is well known that blazars can show variability on a wide range of time
scales. This behavior can include periodicity in their $\gamma$-ray emission,
whose clear detection remains an ongoing challenge, partly due to the inherent
stochasticity of the processes involved and also the lack of adequately-well
sampled light curves. We report on a systematic search for periodicity in a
sample of 24 blazars, using twelve well-established methods applied to
Fermi-LAT data. The sample comprises the most promising candidates selected
from a previous study, extending the light curves from nine to twelve years and
broadening the energy range analyzed from $>$1 GeV to $>$0.1 GeV. These
improvements allow us to build a sample of blazars that display a period
detected with global significance $\gtrsim3\,\sigma$. Specifically, these
sources are PKS 0454$-$234, S5 0716+714, OJ 014, PG 1553+113, and PKS
2155$-$304. Periodic $\gamma$-ray emission may be an indication of modulation
of the jet power, particle composition, or geometry but most likely originates
in the accretion disk, possibly indicating the presence of a supermassive black
hole binary system.
