We were able to book a great flight to Paris using Award miles but have had difficulty finding a return flight. When we look to purchase one-way tickets from Paris the prices are astronomical -- twice or more what a round trip would cost. Does anyone have an explanation for this? I wonder if the website is faulty or if these figures are correct. Thank you.

One way fares are often more than returns, certainly for intercontinental flights.

You could buy a return and throw away the return leg, though airlines really hate that and can charge you extra.
Have a look at other airlines from elsewhere in Europe and see what they charge
You could also look at Norwegian.

As long as you are looking at non point-to-point carriers, the one way is almost always more expensive than the round trip. This has most to do with the market environment and little to do with the distance traveled. I presume you have already used your points so what you are left with are strategies mentioned by hetismij2. With the type of award you had, was it possible to book a round trip or an open-jaw by payment a supplement, which I suspect would have been cheaper than buying a separate one-way flight?

Thanks for the responses, I was mostly just in shock and figured the website had to be malfunctioning! We have more miles to use, but can't find a return flight that doesn't extend our trip by several weeks. I'm looking at alternative airports, any advice there is appreciated! Since we've already booked the outbound flight, I'm not certain how we'd add a return flight but I'll see if DH knows how to do it. Thanks again.

How about looking for a return ticket using miles from say Germany, Switzerland, Amsterdam, etc. then take a cheap flight to there from Paris to get home?

Look at AerLingus. Their one way flights tend to be cheaper than others.

>>>We have more miles to use, but can't find a return flight that doesn't extend our trip by several weeks. I'm looking at alternative airports, any advice there is appreciated!<<<

If you want advice on this, you need to state your airline alliance, dates, cities. No point in people suggesting things that won't work for your airline/destination.