I can understand how difficult the situation would be for the teenage orphan to lose our dear ones. But as it is rightly said that we should move on with our life - I can understand here the situation is quite difficult but it's recommended that we need to somehow move forward with our lives.
Some of the motivation that I'll provide to the teenager would be - that life has up and downs but these downturns are not for always so move on and accept the fact that we have lost our dear ones.
Once a person accepts that he or she has lost the dear ones that only can they focus on other works. I'll, also encourage the teenager to focus on his studies because as at times the teenagers get distracted and tend to drop out of school or college. My focus would be to motivate him to continue on with his/her studies as this is very critical for him to grow in future and understand things how they work and what we need to do to survive in this dynamic world.
The other motivation would be around being connected with the other family members. The family is important and sometimes during these hard times the person feels alone and tend to leave all the family members around. This further leads him to take wrong decisions in life. So, the motivation would be to stay connected with other people in the family - go visit them during weekends as this will help to get out of the recent incident that has happened in life.
Finally, I did like to share with him motivational stories around how people during tuff lifetimes are able to get out of it by focusing on things that they need to do. Sometimes the encouraging words and motivational stories pump up the individual to get out the situation he or she is in and get back on track of life. So, I did like to share great inspiration stories so that the teenager can relate that life is not all about good - we do face bad times and they are not there for always. Bad times comes and goes it just the part of our life.
The words depend solely on the situation at hand and the message you intend to pass across.
If the teenage orphan is depressed and tired of trying to succeed and be established. You could tell him/her that, "it gets better in time, life brings challenges our way to toughen us up for what awaits in the future. How we handle these challenges would determine what the future would bring. But at the end of the day, the challenges would end, and where you would be by then, is solely determined by how you handled the challenges you faced. So faced them head on, and don't be afraid to fail. Just get back up everytime you fall and you would see yourself at the top"
It's never fun losing one's parent(s) at a young age. The feeling could be suicidal and there is hardly anything you could do to stop the child from grieving.
First, the teenager would need you to be there. Like be the shoulder they could cry crying on.
Then, acknowledge that the parents are gone and that nothing they say or do can bring them back. Acknowledge that their feelings are normal. It's not normal to cry, normal to grief. You have to acknowledge their presence and listen to them speak and talk about the importance, the role the dead played in the life of the teenager.
Much of what you need to do is but talk actually, but to listen. To offer your listening ear and to understand the emotional toil that goes with the loss of a dear one.
What you need to do is to validate their feelings and not to trivialize their grief.
I'm limited to today what I can provide as an answer because you said 'words' and not 'actions' , what to do.
I hope this helps however!