The Chaser (2008)

Joong-ho, an ex-cop who was fired for corruption and currently works as a pimp, notices that some of his girls have gone missing. While he's trying to figure out if they've run away with  money he's fronted them, he realizes they all have something in common. The last caller who booked them had the same phone number - and he's just sent another girl to meet this guy.

In fear that the customer is selling his girls, Joong-ho calls Mi-jin, who is currently in a car with the customer. Joong-ho asks her to not let on that there is an issue but to let him know the mans address when they get to his house. She agrees and Joong-ho heads toward the part of town where Mi-jin was supposed to meet the client.  But he never hears from her.

Worried that another of his girls will be stolen, he starts driving the streets and locates her car.  A short while later a minor fender bender changes everything and the chase is on.

This is a violent thriller and I don't want to reveal much about it as you'll enjoy it more if you go in blind.  Joong-ho is the protagonist but he's not a good man.  Even as he chases the man down, you know he's doing it because he's concerned about losing money on his girls rather than their safety.  The introduction of the seven year old daughter of Mi-jim complicates things but also brings some humanity to the main character.  Thankfully the child doesn't get in the way as Joong-ho brings her on his search into the seedy parts of town, although he does try to keep her from seeing him beat the hell out of people. How sweet of him.

If you're looking for a good thriller, can handle some uncomfortable violence, and don't mind subtitles, I'd recommend this one.