Generally, you are able to go view apartments before you really have a roommate. However, given the high rent prices and the speed that apartments go on and off the market, it is recommended that you at least have some roommate options lined up. 

You will be expected to cover an entire lease on your own, or have a roommate to co-sign with you. So to not waste your own time and the designated partner's time, it's best if you are a bit more mature in the roommate search phase before you start seeing apartments on your own. 

If you are interested in a co-living apartment, then you don't have to worry about lining up a roommate before, since the roommates will already be provided and you will only be responsible for your own room.