How soon should I expect to see results?

There is no definite answer to this one. Every individual has different muscle types, level of dedication, and other variables. However, with consistent practice, the average time it takes to start seeing good results is about eight weeks. Keep in mind that nutrition can also impact your results. Training your traps (and all types of workouts for that matter) should go with proper nutrition if you want better results. Check out recommended foods to eat pre-workout as well as post-workout.

Do trap exercises increase neck size?

Trap training does impact the neck since the muscles are near the back of your neck. Ultimately, trap workouts increase the space between your delts and neck. However, since they are not directly targeted at the neck, the impact is minimal. If you are aiming for a bigger neck, you need to do isolation exercises that target the neck.