  Blazars present highly variable $\gamma$-ray emission. This variability,
which can range from a few minutes to several years, is also observed at other
wavelengths across the entire electromagnetic spectrum. We make use of the
first 12 years of data from the Fermi Large Area Telescope (LAT), complemented
with multiwavelength (MWL) archival data from different observatories and
facilities in radio, infrared and optical bands, to study the possible periodic
emission from 19 blazars previously claimed as periodic candidates. A
periodicity analysis is performed with a pipeline for periodicity searches.
Moreover, we study the cross-correlations between the $\gamma$-ray and MWL
light curves. Additionally, we use the fractional variability and the structure
function to evaluate the variability timescales. We find five blazars showing
hints of periodic modulation with $\geq$3.0$\sigma$ ($\approx$0$\sigma$
post-trials), with periods ranging from 1.2 to 4 years, both in their
$\gamma$-ray and MWL emission. The results provide clues for understanding the
physical mechanisms generating the observed periodicity.
