I wouldn't advocate massage in the acute stage, but you might give it a try later on. What's today, Day 4? Let me know how you are progressing...do you still have pain and limited range of motion? You should begin some strengthening exercises. Try these:
Quad Sets: sitting down with the knee fully extended, contract the quad to press the back of the knee into the floor (these are kind of hard to explain in words only, bear with me

....)
Straight Leg Raises: lying on the floor with the knee extended, lift your leg up (keeping knee extended) to a ~45degree angle, hold and lower.
You can do these in sets of 12...rest 60 seconds between sets. Make sure you have no exacerbation of pain when doing the exercises. Stick to just the quad sets if you still have pain and tightness.
I hope this will help you...it is difficult to give someone therapeutic advice when you have not seen them, though. I failed to ask if you had any swelling or bruising in the area of pain? This would indicate a more severe strain. Being that you walked for 20minutes on Day 2, I assumed it was just a mild strain.
Until you have absolutely no pain, you can wear a compression bandage (elastic bandage, usually dark beige colored, that you can buy at most pharmacies)...
Hope you are doing well
