Observed properties of stars and planets in binary/multiple star systems provide clues to planet formation and evolution . We extended our survey for visual stellar companions to the hosts of transiting exoplanets by 21 stars , using the Lucky Imaging technique with the two AstraLux instruments : AstraLux Norte at the Calar Alto 2.2-m telescope , and AstraLux Sur at the ESO 3.5-m New Technology Telescope at La Silla . Typically a sensitivity to companions of magnitude difference \Delta z ^ { \prime } \approx 4 is achieved at angular separation \rho = 0.5 \arcsec and \Delta z ^ { \prime } \ga 6 for \rho = 1 \arcsec . We present observations of two previously unknown binary candidate companions , to the transiting planet host stars HAT-P-8 and WASP-12 , and derive photometric and astrometric properties of the companion candidates . The common proper motions of the previously discovered companion candidates with the exoplanet host stars TrES-4 and WASP-2 are confirmed from follow-up observations . A Bayesian statistical analysis of 31 transiting exoplanet host stars observed with AstraLux suggests that the companion star fraction of planet hosts is not significantly different from that of solar-type field stars , but that the binary separation is on average larger for planet host stars .