Balchik is a city in Bulgaria, located on the Black Sea Coast, in the Dobrich Province, with around 12,000 people living in it.
When standing on or near the beach, try to walk up the hill via the town or follow the main road (which is called Ulica Panorama Pat, Ulica Magnolia and Ulica Primorska - the name changes but it's the same road - number 27). However, this main road is going through the town and traffic that bypasses Balchik will not use it. You can hitch it, but there won't be many cars. It might be better to walk up to E87 (check Google Maps here).
Balchik is not a very hitchhiker-friendly place when it comes to sleeping options. Lots of large and expensive hotels and the beach mainly consists of rocks. There is, however, one very very nice place to pitch your tent (and maybe the only one in Balchik). To get there, walk east on road number 27 until the road splits and the main road is going up the hill, this is where you can see a sign pointing to 'Topola Skies Resort'. Don't follow number 27 but take the road that goes next to the sea (there are some trees in between this road and the sea). Walk around 500 m until you see an old lighthouse. Continue on this road (don't go to the lighthouse) and walk 300 m further. Near the sign that marks the end of the town of Balchik, there is a very small path through the trees that will bring you to the beach. There is sand on this beach :) This is a very nice place to put up a tent or sleep under the stars if you want to sleep on the beach. In the morning some Bulgarian families might come here to swim, but they're only going to this particular spot because they want to escape the bustle of the touristic beaches of Balchik and are very unlikely to bother you.