I tried with "mMap.animateCamera( CameraUpdateFactory.zoomTo( 17.0f ) );" but it didn't work for me. So I used this animation for zooming in on start.
LatLng loc = new LatLng(33.8688, 151.2093);
mMap.addMarker(new MarkerOptions().position(loc).title("Sydney"));
mMap.animateCamera(CameraUpdateFactory.newLatLngZoom(loc, 18), 5000, null);