OMG! I am so sorry! No words can express my shock and sorrow. I know how very close and dear cousins can be. Many are just as close as brothers and sisters. I know exactly what you are going through. I lost my cousin a few years back in the same way (except that it wasn't on purpose). My 15 year old cousin was walking to school when a huge bus zoomed on the road and ran over him. (The bus driver didn't see him as he was a "small" (in size) boy and the bus was so high, nevertheless, the driver is in jail for life now. His shirt got caught under the wheel and the bus dragged him for a while. His ribs were all crushed and he died instantly. That was the worst loss our family has ever had. Its been about 7 years now, but my aunt still cannot bear to hear his name. She just bursts out crying. He was her first child of 5, and her dearest little boy. He was my mom's favorite nephew, and my brother's favorite cousin. We were in total shock because no one expects such a sudden death of a 15 year old child.
I am so very sorry for you terrible loss and pray that the teenagers that did this to your cousin, get what they deserve both in this world and in the hereafter.