Blazars are candidate extragalactic cosmic ray accelerators, and could be confirmed as such by multi-messenger astronomy. Fermi-LAT and IceCube have been used to search for neutrinos in time correlation with the gamma-ray emission from blazars, which has been observed to flare by orders of magnitude. In my PhD thesis, I first focused on TXS 0506+056, whose flare in 2017 coincided with arrival of the neutrino alert IceCube-170922A. I also extended the principle by "stacking" the signal from multiple blazar flares, as their individually undetectable neutrino emission could still be discoverable this way. I selected 179 bright and variable blazars, divided them into two classes and assigned them statistical weights.
