One of the most straightforward approaches is to increase a value of the android:padding
attribute:
<SeekBar
android:id="@+id/yourSeekBar"
android:progressDrawable="@drawable/seekbar_progress"
android:thumb="@drawable/seekbar_thumb"
android:paddingTop="@dimen/your_topPadding"
android:paddingBottom="@dimen/your_bottomPadding" />
Another possibility: make a custom thumb and increase its background's size by adding e.g. transparent border.
You can also use this library for more complex SeekBars
.
In addition, there you have a nice tutorial describing a custom SeekBar
creation.