Hi! Your son sounds a lot like my son. At my sons 2nd birthday he had a vocabulary of "mama, dada, and noo" I of corse was very concerned, as everything I looked up on delayed speech led me to autism or other special needs sites. My pediatrition recommended early intervention. I personally didnt find them to be a great help, as I was already using the tactics that they were introducing. Some of the things I did was I made pictures of some of the things he likes, such as juice, snacks, his bed, tiys, books, puzzles...I put them on the fridge so he could point them out when he wanted them...eventually he began saying the word (or at least trying to) with prompt. Another thing to try is putting him in aplaygroup or some sort of interaction with kids that are his age..I say his age because my son has an older brother whom he didnt seem to pick up any vocab from.
Now that my son is 3, I have taken him to preschool screenings which are free through the public school system (as is Early Intervention, ask you Pedi), and he was determined to meet the criteria for speech service twice a week. He absolutely LOVES it because it is at the school and they pull a few kids out of their class when I drop my son off for his speech. Now he is talking constantly, many people still cant understand him..but he is coming along. I have spent many nights awake worring about whys what ifs and oh mys...but now I realize that he will speak hes just doing it at his own pace!
Good luck, and dont worry, soon your little guy will start talking!