When you are ready to finish off the Popstar series of missions (only available after doing the bus route scam) bring up the mission on your phone and follow the waypoint to a park bench, where you will begin your next mission.
A van will appear, and you will have to jump in and wait for Popstar to show his face as the first step in the mission. When you hop in, time will fast forward some, until Popstar comes out and gets into his fancy car. You will now have to tail Popstar without him noticing you. A suspicion meter will appear on the left side of the screen, and it will fill when you break too many traffic laws, speed too much, or get too close to the target vehicle. All in all, this section is easier than it is in similar games, so you don't have to worry all that much about getting too close to the target or whatnot. Simply tail him going an average speed and make sure that you are staying on the correct side of the road - remember, in Hong Kong the legal side of the road is the left, not the right!
Follow Popstar for a little while and he will eventually lead you to the docks. Exit your van, climb onto the roof of the building to the right, and take cover behind the outcropping wood by hitting the left bumper. Bring up the camera just like you did when photographing Amanda, by hitting up and using the left trigger to aim and the right trigger to snap pictures. Only this time, the subjects of your little project will be of a decidedly more illegal variety. Snap a picture of Popstar nabbing the drugs from the trunk of the car below and file it in evidence for Teng.
After snapping the first picture, hop down from the top of the building and take cover behind the sheet metal. You will now have to snap a second picture. Take out your camera phone just like before and wait until the drug dealer hands Popstar the case. Stay behind the sheet metal and wait for all of Popstar's crew to disappear behind the docks until the waypoint marker appears on the stairway ahead. Quickly rush out and run through the waypoint. A new mechanic is about to be introduced here without much warning, so be careful and pay close attention. You are about to begin a persuasion sequence. These sections will pop up now and again, and will allow you to pass through guarded areas without causing a ruckus. In this case, Wei will begin to stumble and slur his words as if drunk. One of Popstar's guards will approach you and demand that you leave. At this point, a prompt will quickly pop up at the top of the screen asking you to hit the Y button. If you get it right, Wei will stumble past the guard, miraculously summoning puke from his stomach somehow to pretend to be drunk. Seeing your miracle puke, the guard will let you pass, clearly afraid of your mystical powers.
Run past the guard and climb over the side of the boat to the left of the ramp. Climb up onto the crates on the back of the boat, being sure to grab the jade statue along the way. Hop up to the top of the boat's cabin and take cover behind the wooden wall on top. Pull out your camera and get ready to take another picture. Zoom in on Popstar and his contact, who will be meeting up in the hooded boat ahead, the one lit by all of the lanterns. Wait for them to finish their conversation and zoom in, getting ready to snap the picture. As soon as Popstar pulls the gun on his partner, snap the picture and send it to Teng. Call her as Popstar flees in his armada of boats. Teng will now have all of the evidence she needs to bring Popstar down, not just for drug trafficking anymore, but for murder as well.
Leave the boat, run back down the dock, and head back to your chicken van. You will now need to take the van back to Teng's HQ, but you won't have it easy. The police have been alerted to the murder, and they're after you! They will come both in the standard cruisers and on their speedy motorcycles. Luckily for you, you can easily ram the motorcycles off of the road with your hefty van, and the police cruisers should be easy enough to lose or ram off of the road. Get rid of all of the cops, and follow the waypoint on your HUD minimap back to Teng's hideout. Park your under cover van in the garage, and you will have completed this mission.