The rapidly oscillating Ap (roAp) stars exhibit short time scale photometric and/or radial velocity variations, which are most important to test current pulsation models as well as our assumptions of the atmospheric structure characteristics. In addition, their chemical peculiarity makes them very interesting for probing stellar formation and evolution in the presence of a global magnetic field. To date, only a limited number of about 45 roAp stars are known. In order to increase the sample, we obtained photometric time series of 20 good roAp candidates to search for pulsations. We present the time series analysis of about 60 hours of CCD photometry taken at the 1 meter Austrian-Croatian Telescope (Hvar Observatory) and derive effective temperatures for the programme objects. The upper amplitude limits of the Fourier spectra are typically below 2mmag in Bessell B with one good candidate for follow-up observations to find possible pulsation. In addition, we present a list of further roAp candidates, worth to be (re)investigated.