I think OC's are fine and I have been writing them since day 1. But, as was suggested, it's really a good idea to put something into your other characters. Don't get stuck into this trap of making your original characters Mary Sues. That annoys a lot of readers and makes them want to leave the story screaming.
A professional writer actually gave me the following tip for writing Original Characters. She suggested to me during the time when I was writing my novel to write down certain aspects or characteristics of my characters in an outline form and never diverge away from them when writing the plot. Give them positive and negative character traits, don't make them too perfect or with too many problems (the damsel in distress syndrome). If you want to write effective OC's, try something like the following outline. (Just for the sake of example, I am tossing in one of my own OCs, a minor character from my novel.)
Name of character: Julius Birmingham (Brother Benedict)
Age of character: 30
Physical Description: Light brown / blonde wavy hair, blue eyes, youthful expressive face. Julius is shorter than the other monks. He is about 160cm tall, somewhat heavier, close to 70kg, has dimples when he smiles and freckles.
Personality: energetic, agile, contemplative, curious, friendly, but has moments when he can be very stern and to the point. He doesn’t trust people as much as he should, but is still learning. He is also fairly new to the Order.
Title / Status (if any): Monk / Brother Benedict
This isn't exactly what you should use, but it does give you a rough idea as to how to incorporate original characters into a story. It was also the same concept I used when writing my novel. Since you are a younger writer, it is vitally important for you to try different kinds of things or tips to see what specifically works for you. The more concise and real you make the OCs, the better your chances of getting a consistent audience.
One of the challenges I see with a lot of younger writers (that is writers in their teens) is the entrapment of saying 'oh well, it's only fan fiction, I don't need to focus on spelling, grammar, or even research. It's too time consuming.'
Many readers, specifically older readers want to read something that is not only grammatically correct, but also realistic. Even Muppet pieces have to have elements of realism in them, otherwise the chracters risk going out of character. Kermit would not go and karate chop Animal anymore than Piggy might start singing 'Kumbaya' in the swamp.
As for getting people interested in your work, I don't really know what it is I can suggest you do. My experiences are with just about every story I have ever written and posted somewhere, the number of reviews always tends to go on a downward spiral after chapter 3 or 4. I get my steady readers, the ones who read and review each installment and then I am pleased with the specific details they put into their comments. The thing that I think you need is to find the motivation to write something and not to worry about how the response is going to be. I know that that is really hard, but sometimes the people who are not the most popular can really go and crank out some of the best writing I've ever seen. It's been done, and amazing writers are constantly blowing my mind with their works.
The bottom line is, write for yourself, and enjoy the act of taking an idea and going with it.
When I started writing fan fiction some 15-20 years ago, the thing that I fell into was this idea that I had to do what everyone else told me. I had a story idea that was AU (Alternate Universe) and someone came to me and said 'you can't do that, Yva, it contradicts the universe you're writing'. I heeded those words and today, some 14 years later, I have gone back to the story and have actually completed it. The story is presently being posted at fan fiction net and it is probably one of my proudest efforts, because it takes a bit of the past and is encased in the present. The point to that digression is, don't sacrifice too much of yourself for the sake of keeping readers. Write whatever may work for you and savor the joy of it.