unfortunately the tear drop you are referring to is highly genetic depending on "what ya momma gave ya." That being said the anatomy of the teardrop is the insertion points of the vastus medisalis, lateralis, rectus femorus, and sartorius. as previous posts have mentioned front squats, hack squats, and the controversial leg extension with varied toe positions will target these fibers the greatest- per emg testing. Anything that will target these muscles as best ya can in a controlled fashion will do. If ya have long tendons and short muscle "bellies" this part of the thigh can and is very difficulty to attain. On all the mentoned exercises ya must go to full lock out of the knees so be careful of those joints. The biggest part of the muscle which is much more proximal to this area will try and recruit these fibers first so ya must concentrate-regardless of weight used- while performing these movements. Best of luck.