Teenagers are infamous for their lackadaisical attitude and impulsive behavior. While these may seem contradictory, they actually have a strong connection. Teenagers live in the present. The future is remote and surreal to them. When you try to motivate your son, set short term goals of his choosing - with some guidance. You will find boys are motivated to do what they want, not what you want.
Observe his interests. Do not ask him what interests him; simply watch. See what he spends most of his time doing and what topics make him perk up. Your son will be most motivated to pursue things he already has an interest in.
Determine whether he is people-oriented or goal-oriented. Offer incentives that cater to his personality. If he is people-oriented, plan an outing to a movie with a group of his friends. If he is goal-oriented, create a list of milestones for the coming months. If he reaches those milestones, congratulate him and discuss what his hopes are for the future.
Remove distractions and luxuries. If he has everything he wants, he will lack motivation to pursue anything more. To your son, luxury items are things like his phone, computer, TV, video games and going out with friends. Reward activities such as studying, doing well on a test and helping with chores by reinstating those luxuries.
Make lists. If he needs motivation to do chores, create a master list together. Check off the accomplished items as he completes them. Does your son need motivation to do well in school? Help him create a schedule that details how long he should study in each subject and what assignments are do. You will be his coach throughout this as well as his cheerleader. Your son needs to know that he has what it takes.
Try to keep the conversation open.
Resist the temptation to perpetually nag or scream at your son. This will have the opposite effect. Boys will sometimes purposefully fail to make a point. Try to ask leading questions so that he finds the motivation himself. If he is doing something to please you, he will not follow through. Talk to your son in a place other than home, like a restaurant or park.