I'm guessing that in addition to your delts not growing, that you also have a hard time getting a good "feel" to them while training and getting a good pump in the delts. What you probably need to work on first and foremost is to develop a good mind/muscle connection with your delt muscles. Once you've developed this, then things such as mass and strength should increase for you.
To develop a good mind/muscle connection, I believe you should try a couple of things. Do some good warm-ups and stretching before you hit the weights, then go into a light set of high reps of side laterals then the same for rear laterals. Then pyramid up in weight over 3 sets with either seated dumbell presses or barbell military presses. THEN go into your heavy sets.
When training delts or any bodypart for that matter, you need to squeeze the hell out of them -- don't just go through the motions of the exercise and feel that because you went to positive failure that you got the most out of that set. Even before I start a set of let's say military presses, I've got my delts, arms, traps, lower back and abs, legs, feet planted firmly on the floor, and hands (squeezing the bar like crazy) squeezed and flexed, THEN I start the set and maintain this squeeze throughout the entire set.
I'm assuming you're a natural trainer like I am, so don't go overboard with your total number of sets for delts. But, like others have said in this thread, don't do too little either since the delts are very dense muscles and need a little bit extra volume to get the job done. For myself, I do a total of 11 to 12 sets; depending on how I'm feeling it that day.
Eat 7 times a day CONSISTENTLY and get enough rest, and you should see some results in a few months (be patient).