Annata,
Just because you join an online program, does not mean you lose all contact with your peers and professors. In fact, I have found in my experience, that communication increases greatly. I am planning on writing an article on this in the near future (or I would like to), but because there is limited space in the distance learning tips topic, it might have to wait. So, in the meantime, I will briefly answer for you.
In most programs, the professor of each class will provide you with their office hours and telephone or email so you can contact them freely. However, if they are not a campus professor as well as online, they may not have an office and they may give you a personal email contact or home office phone instead. I have had both happen and have used these resources when doing my thesis, or have had a question on a paper or assignment as well.
As far as the student ratio goes, I believe it is actually smaller then that of large university. I attended the University of Buffalo in New York for my Masters which was completely online. The actual lecture halls on campus can hold a couple hundred students while my online courses could only hold about 25 or so. I was able to develop much closer relationships with my peers as well as it was easy to keep track of names. In fact, many of my professors' gave us our first assignment on peer introductions and discussion. Part of your grade depends highly on communication and discussions which is done on a daily basis.
Some professors even set up private chat times to discuss any issues you have with the program or class. I was even given an advisor for the program, just as I would be on campus. It was really reassuring to know that I was receiving the same (if not more) attention from my peers and professors with online learning as technology these days seems to overrule many other forms of communication.
I hope this helps for now and again stay tuned... :)
Thanks,
Sarah