You could look up www.escort.cz - It has listings for clubs and independent girls. It gives the girls by age, height, weight, breast size, languages spoken etc. Some can be a bit out of the city but Prague has a great public transport system so it won't take long to get anywhere.
Avoid girls that proposition late at night in the street-especially the gypsies of which there are a few-its possible they might have someone waiting to mug you.
Have fun.