track down
To search for or pursue someone or something until located or captured. A noun or pronoun can be used between "track" and "down." I've been trying to track down people from my graduating class for our high school reunion. The police tracked down the fugitive to an abandoned warehouse on the outskirts of town. My son really wants this particular toy, so I was wondering if you could help me track it down.
track someone or something down
to search out where someone or something is. I don't know where Anne is. I'll try to track her down. I'll track down Anne for you.
track down
Follow successfully, locate, as in I've been trying to track down that book but haven't had any luck. This term alludes to the literal use of track, "follow the footsteps of." [Second half of 1800s]
track down
v. To pursue someone or something until found or captured: I tracked down the book I was looking for. The fugitives were missing for a month before the police tracked them down.