The actual number of bitcoin users cant be known becasue the limit of the bitcoins is not reached yet you know if we reach the bitcoin limit
we will know how many users there are this is not strange why cant you think about this by your self.

Its better not to waste time in knowing that how many are actually using it, instead that time should be invested in earning bitcoins as no one can get accurate results.

It is right, we can't calculate the users number of bitcoins, but we judge it because of the bitcoin price, I mean its price show us what is going with bitcoin. Also it is true, now majority have awareness about bitcoin, and the number of the bitcoin users increased within last 2 or 3 years, and now it is continuously growing,So we have only one way to predict about it.

We can see it on the daily volume of BTC.
In addition there is actually a greater popularization day after day of Bitcoin crypto currencies.

It is difficult to get even an approximation  of the real value, and I would be surprised if  anyone managed  to get a good number for it , without very high error margins, of course..

all of these are going to give us a vague idea of how many people are using bitcoin. and none of them can help us speculate about the exact number of them.
there are so many data that you can use for this and you have to use them all together.
- daily trade volume
- number of transactions per day
- number of new wallets created on services like blockchain.info, Coinbase,...
- number of people using different online services that accept bitcoin like Gyft, Steam, ....

for a closer estimate you will have to start asking people in the street and extrapolate the data.

By far not. If you look at 2% of the people, then you are talking about 140 million people. And that's definitely not the case. If we at some point in the far future manage to have 1% of the world population to use Bitcoin, then that can be seen as a great mile stone. 1% equals around 70 million people.

We can't say because there are people having numerous wallets and some have abandoned using BTC so it really can't be exactly said how many people use BTC

I think certainly bitcoin users would be more than 400k., even if you look at the total users in this forum alone is more than 600K users. certainly out there are more users

Be 5% of people worldwide are using and know bitcoin . Since news spread very fast across the world so while taking greater and greater and use it and most of those who invest with them online . Maybe in a few years bitcoin is further identify these people and many more can they use it and do earn bitcoin.