In a speech on BBC world live from KL(at 18th/09.35 UTC) the Malaysian government confirmed the following were involved in the search for this jet,
http://www.bbc.co.uk/news/world-asia-26625473
Australia 3 P-3W
1 C-130J
Japan 2 P-3C
2 C-130H
1 U-4
Korea 1 C-130
1 P-3
New Zealand 1 P-3K
United Arab Emirates 1 C-17A
1 DHC-8
United States 1 P-3C (this was 161764 RC-764 last week)
1 P-8A This is operating from Perth,WA
Most of these assets are operating from Malaysia. Butterworth is likely to be a major operating location.