Hanoi is a city in Vietnam.
Hitchhiking inside of the city
In Hanoi a hitchhiker has it only easy when alone, as there are motorbikes literally everywhere and the few cars are surrounded by them which makes it in most parts almost impossible for them to stop. Hitching a motorbike is surprisingly very easy. The drivers will often take you without a helmet but keep in mind that it is the law in Vietnam to wear one on a motorbike. Hitching with cars is also quiet easy when choosing the right spot. People are very open to take you, if they can. Approaching them at traffic lights is a good option. Another option is finding a less crowded street and waving at the cars that are not surrounded by bikes. Make sure they have enough space to stop. Some people speak English, having a translator with some key phrases ready (google translate offline) is an advantage.
Getting out of Hanoi is pretty easy if you go by bus to the beginning of the Expressway. It's a good place to get a ride. A quick way to leave to a new destination is to look at the city bus map, many bus lines extend very far out of the city (up to 40km..). Take a city bus that goes to a village that's on your way and you get out of the bus when you're out of the city and see a good spot to hitchhike. If you have time, hitch your way out and meet many nice people from the city.
Towards Lao Cai
If you have time, hitch your way out and meet many nice people from the city. If not, take a bus number 7, 56, 58 or 64 going north. It will be a long ride. At some point (2 km before the airport), the bus will pass toll gate and stop 100 meters after. Walk back to the toll gate and ask people there. I tried walking right from the gate and hitchhiking at the entrance of the highway but no cars go there even it's a logical way to go. They continue straight from the toll gate and turn left then right to the highway. Real highway exist for about 60-70 km and after that is something like half highway, so if your ride is not going directly to Lao Cai (most probably won't), you can hitchhike directly on the road. (by NixyJungle)
The easiest way to get a ride toward the south is to hitchhike at the first Tol Gate on the CT01 Highway google map. To reach it take the city bus to the bus stop "Đd UBND Liên Ninh". In Hanoi Google map can help you find the best bus route for you. For a direct bus ride take any 06 bus route (06A, 06B, ect...)starting at train station named "Ga Giáp Bát". There is actually 2 bus stop for this train station, That's the one after (further away from down town) that have the buses 06X. The bus ride cost only 8000 VND (2018). Once you reach "Đd UBND Liên Ninh" bus stop, the Tol Gate is just 1km away and easily and safely accessible by foot and the staff very friendly.