I think some whales are behind it to pump price near 500 where some of them have bought coin in early november. And also positive psycology of traders is also taking part in this rise.
Not sure if the people who are currently are buying are only whales. I think people are tired of waiting for the right moment to buy, and thus they buy right now, to not stay behind and see the price go up while they haven't bought anything. I know how that feels. That feeling sucks. Just make sure you buy right now.
There are much more people posting here than there were last summer. Loysof people who stopped posting for months have now started again. That's a sign that people are regaining interest in bitcoin, and those people will be buying and pushing the price up.