If you have a number of them they will start to venture out once they feel safe and happy in their enviroment. Mine are very often out day and night, merrily swimming up the front glass......and they have alot of hiding places if they don't wish to be seen. Give them time. Some are shyer then others (Decorus are very shy), some simply don't want to be out in the daytime due to their nocturnal preference. Another thing that can help is lighting that is not strong. In a deeper tank the light won't be very bright near the bottom and they feel much happier with that then strong light.
P.