The identification of growth precursors in reactive plasmas is of major interest for any optimization of plasma processes. Various diagnostics might be employed to detect important radicals in plasma chemistry. However, the species which produce the highest signal in a specific discharge might not be relevant for film growth since they are not efficiently pumped by the substrate surfaces. This paper describes concepts to characterize the plasma chemistry using reactor parameters, which might be compared with diagnostics such as mass spectrometry. In addition, relevant methods to study surface processes such as the roughness evolution during thin film growth are illustrated. The search for growth precursors and material synthesis is illustrated for two examples: (i) the formation of nanoparticles in low pressure reactive plasmas; (ii) the generation of higher hydrocarbons in microplasmas operated at atmospheric pressure.