People frequently travel all the way between Kelowna and Osoyoos so rides out of Penticton are frequent.
South towards Osooyos
Highway 97 is your best bet. The intersection of Channel Parkway and Green Mountain Rd is a good spot to thumb. Just get on Parkway, to head south. Rides are fairly easy to get here.
North towards Kelowna
Eckhardt Ave heads NW and becomes highway 97. Once you are up out of the city center, the hitching is really easy. The corner where Eckhardt becomes 97, after the bridge, works well.
Just ask to be dropped near the highway if you aren't staying overnight.
Places to avoid
Accommodation and Sleep
There are camp grounds around.
Other useful info