I would not really recommend the Lake neighborhood in San Francisco for singles, mainly because it is a little pricey. Even a simple studio in Lake will cost you at least $1300/mo. Most singles I know can't afford those kinds of prices and if they can would rather move closer to North Beach and that area if they are going to pay $2000 per room.
Also, just to the south and west of Lake you can find cheaper digs in the Richmond district.
