One way to find the source of leaks is to run water over the roof using a hose, and watching where drips will occur. However, the fact that such task will require you to go up on the roof presents hazards, and should be done only with extreme care and caution.
Besides, there are cases when this method may not lead to the leak source, and a closer inspection of the shingles and other roofing parts is needed. Leaks are usually caused by broken flashing, damaged shingles, and plumbing penetration. To ensure a thorough inspection, consider hiring a skilled roofing contractor in Sunnyvale instead.