Baja is a strange place when it comes to American community. I'm not sure if it because everything is so spread out and you need a car to get around esp. if you go outside of TJ or it's the fact that most of the Americans living in Baja are from the West Coast and known for not being so neighborly. If you have lived in other parts of the U.S. and then live in California, Oregon or Washington state one thing you notice is that people don't get involved with their neighbors. I live in San Francisco for several years without knowing my neighbors and the same in Los Angeles and the Portland area.
If you've visited other areas of Mexico with Americans living there you will find those communities much more cohesive than anywhere here in Baja Norte. I live in Rosarito in a big building with many Americans and most of them don't want to get involved with anyone and stay inside the majority of the time. I've lived in Tijuana and Rosarito for over 2 years and most of my friends are Mexican. You're probably better off getting to know Mexicans because if you have some problem while living here chances are a Mexican national will be of more help than Americans esp. since most don't speak Spanish.