Head towards the marker located in the North-Eastern part of Uptown which is the van that you have been following in the fourteenth mission of the game. Interact with the marker to connect to your inFamous Paper Trail profile. If you have performed all of the steps, on the internet page, properly (locating the graphic file on the hard drive and viewing it) you will be allowed to start the fifteenth mission and it concerns tracking down, and destroying, the remaining vans. Press UP on the D-Pad to start the mission.
As you probably have noticed, on the map of Seattle, there appeared four new markers - three of them are in Uptown and one in Waterfront. Head towards one of the vans and, after you get there, locate the vehicle inside the marked area(you will have no problems doing that, because each vehicle is parked in a well-exposed spot). You need to destroy each one of the vans and the easiest way to do that is by firing the strongest attack, available after you press R1. In the same way, blow up the other three vans.
Finally, return to the starting point and destroy the van that you broke into, during the most recent visit to inFamous Paper Trail Project. Thanks to this, there will appear Celia and you need to pick up the Origami Dove that she leaves. Again, you need to leave the game and log on to your inFamous Paper Trail profile.