Drug or alcohol use. A teen with a problem may have dilated pupils or wear sunglasses indoors, or complain about not sleeping or not feeling well. Valuables may disappear. You may find drug paraphernalia or alcohol containers around the house. You might notice new possessions and money not accounted for.
Doubts are normal.
But persistently low self-esteem is a problem. Listlessness, loneliness, withdrawal, difficulty making friends. In fact, family changes such as a death, divorce or remarriage are times when teens often need some outside help.