A study of plasmonic phenomena produced by silver nanoparticles embedded in a photoactive (poly-3-hexylthiophene):[6,6]-phenyl-C61-butyric acid methyl ester (P3HT:PCBM) bulk heterojunction is performed via spectrophotometric and Raman characterizations. An enhanced absorption of light is experimentally obtained in a 90 nm-thick P3HT:PCBM interpenetrated blend layer incorporating evaporated 5 nm-thick silver nanoparticles on glass/ITO substrate. An increase of Raman signal is observed and correlated to an increase of the electromagnetic field close to metallic nanoparticles. This is confirmed by Finite-Difference Time-Domain (FDTD) modeling considering an organized 2D-grating of ellipsoidal domes. This paper shows also that the use of relatively thick organic blend films as probe molecules upon plasmonic structures does not obscure the Raman response.