  The realtime program for high-energy neutrino track events detected by the
IceCube South Pole Neutrino Observatory releases alerts to the astronomical
community with the goal of identifying electromagnetic counterparts to
astrophysical neutrinos. Gamma-ray observations from the $Fermi$-Large Area
Telescope (LAT) enabled the identification of the flaring gamma-ray blazar TXS
0506+056 as a likely counterpart to the neutrino event IC-170922A. By
continuously monitoring the gamma-ray sky, $Fermi$-LAT plays a key role in the
identification of candidate counterparts to realtime neutrino alerts. In this
paper, we present the $Fermi$-LAT strategy for following up high-energy
neutrino alerts applied to seven years of IceCube data. Right after receiving
an alert, a search is performed in order to identify gamma-ray activity from
known and newly-detected sources that are positionally consistent with the
neutrino localization. In this work, we study the population of blazars found
in coincidence with high-energy neutrinos and compare them to the full
population of gamma-ray blazars detected by $Fermi$-LAT. We also evaluate the
relationship between the neutrino and gamma-ray luminosities, finding different
trends between the two blazar classes BL Lacs and flat-spectrum radio quasars.
