I am 18 and I have had acne on my chin and cheeks for years. What can I do to get rid of it?

See your physician. It is better to determine what kind of acne this is before treating. If it is hormonal, it is treated differently than cystic or vulgaris. Go see your physician for a diagnosis and a plan.
See dermatologist. If you have tried over the counter products, prescription creams can help. Laser is effective to reduce acne.And for severe chronic cystic cases Accutane is an option if nothing else works.
A doctor can help. For treatment of acne, over-the-counter benzoyl peroxide gel/cream is quite helpful. If desired, a doctor can add an antibiotic gel/cream such as Cleocin (clindamycin phosphate) gel. If more help is needed, prescription retinoids such as Retin-A or differin gel can be used instead of benzoyl peroxide. Oral antibiotics such as tetracycline can be used also. If acne is quite severe, a dermatologist might use oral accutane.
Many options. Unfortunately there is no cure for acne and it can be quite challenging to get under control. Otc washes and acne treatments containing benzoyl peroxide, salicylic acid, glycolic acid can help. Microdermabrasion, chemical acid peels, light and laser treatments, photodynamic therapy can help. Oral antibiotics, anti-androgen and birth control (for females), Accutane may be needed.
Hormonal in nature. Have your hormones tested. I recommend acid water of 2.5ph to wash daily and occasionally moisten wash cloth or 4x4 gauze applications. If excessive or higher hormonal level then an endocrinologist comes into the picture. Email me if necessary. My website.www.drernie.co.cc.