Thanks guys for the informative posts and you're right Dr Furst Dunaharm, I should accept that I won't grow the same "style" of muscle as other people.
I will try the different variations of push ups with my weight vest. To explain which area of my chest I need to thicken, this may help; Basically the front of my shoulders and clavicle appear boney and protrude infront of my body because the lack of muscle mass in the upper chest area. I am muscular, but very slim as I tend to do a lot of calisthenics and need to keep fairly light but I want to pack on some size there to prevent the "boney look" lol.
Er... looks like the front of the deltoid to me. Strict presses, incline bench press, incline push ups, hand stand push ups, lateral barbell raises, gymnastic ring work like skin the cats will all help.
ad astra per aspera
Yeah, now that the picture's viewable, it's the anterior deltoid.
Once again - you're using the whole deltoid (including the antr, med and postr regions) with every exercise that uses the deltoid. The incline presses, etc will simply highlight the antr region a tad bit over the others. My point is, if the antr deltoid is AWOL at this point, I wouldn't expect it to turn out like the picture.
Have at it and see what you can do, even a little thickness may fill the area out to your liking.
Without seeing pictures of the OP, I would also suggest that he check his posture and back work. Bad posture makes your chest look terrible in many ways. Over-emphasis on chest and other anterior muscles will make this worse. Focusing on good posture and doing lots of back work- horizontal rows, pullups, deadlifts, barbell rows, etc- will help to fix it.
Again, I have no idea what the OP looks like, but this is what I found with myself- no amount of pushups will fix bad posture, which is what was making my chest and shoulders look so terrible in the first place.
The press is the king of shoulder exercises. Nothing fancy, just you standing and moving a barbell over your head. Used to be in the Olympics, and used to be "the" measure of strength back in the day, before people asked "how much you bench?", they asked "how much you press?".
Yup, definitely the front delt. There are lots of ways to isolate it, but I wouldn't waste your time with that. Spend a year trying to increase what you can press overhead and that should do it.
jfreaksho's advice about posture shouldn't be ignored. Concentrating on 'mirror muscles" without training the back will slump everything forward as those mirror muscles get strong and pull against the weak back muscles.