How can we remove the stretch marks in teenagers?

Laser work. "striae atrophicae", stretch marks, are now being resurfaced with some success using lasers. There are physicains in every metropolitan area who focus on this kind of work. Good luck.
The only way. To make these stretch marks go away is to see a dermatologist or plastic surgeon. They may do surgery or use microdermabrasion or laser to reduce the appearance of stretch marks. These are expensive. Not usually recommended for teenagers because they are not finished growing and the stretch marks will diminish over time anyway.