John Kapelos -- who also appeared in "Sixteen Candles," "Weird Science" and several episodes of "Justified" -- is being sued by Michelle Vlahos ... who claims he used "powers of persuasion" to pounce on her loneliness and her craving for male companionship.

In docs, obtained by TMZ, Michelle says John "utilized his theatrical instincts" to create a position of trust before convincing her sometime in 2006 to fork over money to pay his bills, clothing, groceries and luxury items.

She says they had an understanding he would repay the cash, but got radio silence after repeated attempts to get him to pay it back.