Gravitational-wave (GW) signal were finally detected by LIGO on 14th September 2015. On 17th August 2017, the joint observations of a compact binary coalescence in both GW and electromagnetic (EM) channels mark the beginning of the GW multi-messenger astronomy era. In this talk, I will briefly present the followup searches of possible optical counterparts of GW events. I have developed the observational strategies for trigger search, developed pipelines for image analysis and automatic candidate vetting via machine learning algorithm, as well as contribution to spectroscopic identifications and further inferences. I will show our main contributions (on behalf of GRAWITA and DLT40 projects which I was part of) during the first three LIGO-VIRGO collaboration runs. In particular, we had an independent discovery of the kilonova AT 2017gfo, that is, the optical counterpart of GW 170817/GRB 170817A. Finally, as a postdoc at OKC Stockholm now, I will present my current work within the ZTF survey, the GREAT environment, and our plans for search of future GW counterparts.