The IRS has recently undergone some changes to whistleblower payments, including a sequester on the payment of rewards. Add to that that the IRS is hopelessly overworked, especially during this time of year, and I can't say I'm surprised that you haven't heard anything from them, yet.
The situation may not yet be ripe for you to hire personal counsel to follow up with the IRS, therefore. However, it couldn't hurt and the attorney might be able to get a little more traction. Unfortunately, you're unlikely to get someone involved on a contingency basis. You might consider discussing some kind of blended cash fee/contingency arrangement with qualified counsel.
I have seen cases where the IRS never responds to such reports, so your case is not unusual. I would doubt you could get an attorney to take this on contingency. There is not much you could recover in this case, unless the IRS get tax out of this person.
This is not intended to be legal advice, and is general in nature.
You don't say exactly what your controller of the company embezzled and why the IRS is involved. If this involves so called trust fund taxes (employee withholding) that weren't paid over and/or for which false returns were filed, I think that I would suggest that you get a seasoned tax attorney involved. The company is going to be liable and other persons, including you, may be deemed responsible persons and assessed 100 % penalties. Even if it doesn't involve trust fund taxes, given the size of the theft, I would still have an attorney involved.
I would make sure your company's house is in order. It has been my experience that embezzment takes place in loose internal control environments often times purposefully created so that the company can cheat on their income taxes. The IRS knows this and may come a knockin... The IRS usually becomes involved in embezzelment cases where the business wins settels a civil judgment that quantifies the amount embezzled that is sign off on by the embezzler. Its just a simple matter of seeing if the embezzler reported the amount embezzled on their tax return to establish criminal charges for tax evasion at that point.
While my colleagues have provided great answers concerning the IRS, I am wondering why the company isn't going after the embezzler.
This information does not constitute legal advice and does not establish an attorney-client relationship.