In this letter, we consider a 3D molecular communication via diffusion system (MCvDS) with a single point transmitter and multiple fully-absorbing spherical receivers whose centers are distributed as a Poisson point process (PPP) in the medium. We derive the probability that a transmitted molecule hits any of the receivers within time t. We consider both degradable and non-degradable molecules. We verify the analysis using particle-based simulation. The framework can be used for various applications, e.g., to derive event detection probability for systems where the IMs are transmitted to convey the occurrence of a particular event to trigger reactions at receivers or can be used as channel models for such systems.