Samsun is a city in Turkey.
A good hitchhiking spot is on the highway just near the bus station (Samsun Otogar). It is possible to get to the bus station for free from any part of the town using the service buses run by the bus companies. You just need to look up the bus departure times, and then go to a bus company office (located all over the city) and tell them you have a ticket for a bus (e.g., 1:30 bus to Ankara). If they ask to see it, just say you are meeting a friend at the station and the friend has your tickets. The service bus will take you to the station for free and then you can walk under the highway on the road just north of the bus station, and just jump the barrier to the highway and hitchhike from there. Right before the bridge there is a shoulder that is wide enough for someone to pull over.
Another option: Take the tram to the endstation called 'Gaz'. Walk further until you see a big pedestrian-only bridge on your left side (it says Buyuksehir sizin icin). Walk even further until you see the big hotel and shopping complex called 'Anemon' to your right. Walk even further until you cross a sport-complex (with football and tennis) and a park on your left side, called Dogu Park. Note that all the time of this walking, you will walk parallel with a motorway. After maybe 2,5 km walking, you will see the pillars of a motorway that is not yet finished. Turn right, and walk under these yet-to-be-finished motorway. This is where all the traffic goes through that will surpass Samsun. Start thumbing after the construction sites.
Yes, it is a long way from the center but once you're at this very spot, direct (truck-) rides to Ankara and Istanbul and waiting times less than one minute are not uncommon!
East towards Trabzon
Take a bus going to a replica of Bandirma ship (Ataturk came with this ship to Samsun which marks a beginning of the Turkish War for Independence). Everyone knows it. Bus 17 or 19 go there (ask the driver to be sure). The ship is directly at the Eastern roundabout of the city where you can thumb.
In June 2015, Marion_and_John found that the roundabout was a pretty poor spot to hitch. Bus station is very close by and we attracted a good deal of agressive reactions. We then walked to the Lovejoy mall, about 1km to the east. It is on the main road that crosses Samsun. It is a classical HH spot with gas station and *lots* of traffic. We found a lift in 20'.
See the part above about getting out of Samsun in direction West. Dogu Park is actually a very nice place to pitch a tent, with locals barbeque-ing there on hot summer evenings and children playing. Some locals might have brought there own tent and have set it up in the park too. Police is completely fine with people sleeping in tents in this park. It is just a very cozy place.
In case stealth camping does not attract you in this city, you can still sleep at the Municipal Camping for 15 liras (41°16.241'Nx36°22.367'E, WGS84) about 500m to the east of the replica of Bandirma.