If it is an IRA, it has nothing to do with an employer -- unless you had rolled over the funds from a 401(k), and even there, I don't see how you can roll it into a Roth IRA (It would be a regular IRA).
The problem with calling the IRS is that whoever has that money isn't reporting anything to the IRS unless you make a withdrawal. ... IRA money isn't taxable. And since it is a Roth IRA, you didn't take a tax deduction from the contribution (in return for being able to withdraw tax free later), so it probably isn't going to show up on any old tax returns you have.
Do you have other accounts with say a Vanguard or a Fidelity or an Ameritrade or a Schwab? If so, you can try a few of the big brokerages and mutual fund companies that ring a bell to you, or where you have other accounts. Also, maybe see if you can find old bank statements, or request them from your bank? ... You might see a contribution payable to a financial institution, which will lead you to the account.