My presentation will focus on neutron stars (NSs) and their gravitational wave (GW) emission as a tool to investigate them. In particular, I will focus on GWs emitted by isolated spinning NSs. This kind of signal has not been detected yet, and its detection can improve our understanding of how matter behaves in such extreme conditions (NS core reaches densities higher than the nuclear density). I will give an overview of the different kinds of searches, and I will introduce a new approach using machine learning techniques.