Circular to say evidence is proof?

I think this argument enters into the "weasel words" category unless specific can be given. I've read many antivax arguments that also claim a mountain of evidence that supports their view although they can't come up with any concrete or verifiable examples.

If you have evidence at hand, it is merely a statement of fact.

If you have no evidence at hand, there is nothing to back up the claim that evidence "exists", that it can stand up to scrutiny, and that it supports your argument.

"I have debated creationists about evolution and I have told them that there is a mountain of evidence in favor of evolution, but is this a circular argument?"

No, its not circular. Sounds like the creationists might be gaslighting you so that you start to question your own sanity.

"Perhaps it is circular to use the amount of evidence as evidence."

If all the evidence cross confirms to suggest the same conclusion, then that is a lot stronger evidence than just one piece of evidence. 

I don't see how it's circular, the evidence leads to the conclusion, and the conclusion in no way leads to the evidence. The amount of evidence means that the conclusion is based on overwhelming confirming data, and with more data then it should be easier to find something which falsifies the theory yet this hasn't happened. In addition to the fact that there is more evidence supporting evolutionary theory than for anything else in all of science, there are multiple independent methods which confirm one another. 

Nothing you can say will convince someone who believes in things which aren't supported by evidence, and who possibly/probably intentionally misrepresents things which they use as objections, and continue to do so once this is pointed out to them, and who remain willfully ignorant of the topic whilst pretending to understand it.

Edit: I try not to generalise, hence the use of the word possibly, however I am yet to come across a science denier who ever acknowledges their errors/intentional lies, or who ever corrects their narrative. I'm sure that there are some, but they are outliers.

It is not circular, because the amount of evidence does matter when the different pieces of evidence taken together make the convergence of evidence exponentially greater than the individual pieces. This is precisely what makes the theory of evolution so strong.

The evidence of evolution was not gathered so that evolution could be proved. Therefore, the fact that the sum of evidence has never found a counterexample is not circular reasoning.

The mechanism of evolution, gradualism or punctuated equilibrium or something else is still up for grabs, but "God did it" can not be tested, and is the core failure of creationists imo.

There are enough variable evidence sources and types (eg, your mention of dating, fossils) that the "mountain" is a reasonable metaphor.

If there were just one kind of evidence, and the mountain were recognizably constructed of ant-hills piled on ant-hills, the size of the mountain would rightfully be derided as false evidence Argument by Repetition but that is not the case with evolution.