Used Wrong Yeast.... Final Gravity Too High

I strongly advise against yeast nutrients, unless you are sure that this addition will not be sensed in finished beer even if yeast will fall to eat it. Once I had a batch less than optimal due to this.

First, you can just stir gently. This may sometimes be all you really need.

Second, more reliable way is to add a packet or three (yes, three, really) of rehydrated dry yeast. With three packets, cell count should be enough to finish big beer even in unfavorable conditions. To be more specific, use pitching calculator. Then multiply by 2, because some cells won't do it in wort already with alcohol. Then use cell count from manufacturer to see how much you need.

Third option is one I prefer. Make a new beer with yeast you need. Small one, about 10-12°Blg. Nutrients, aeration, all that. As soon as you have a slurry, transfer new beer to secondary, and slurry to the stuck beer. That way, your yeast will be fresh, active and accustomed to having alcohol in solution.

One can pitch dry powdered yeast directly into a brew. It often works well but sometimes not. In my entire brewing career(?!?) I have never used a yeast nutrient(!?!). Some do, some don't.

I usually recommend making a starter with yeast in sugar solution as this is the easiest way to check the yeast is actually active before pitching. I have used powdered yeast that has not been active and I only discovered it some days into the brewing. If one pitches a demonstrably active yeast culture then that much is certain!

Other have also recommended a good rousing/stirring of the brew and any sediment to bring any active yeast back into circulation. Yeast needs oxygen to grow so some aeration of the wort is (at least initially) optimal. If one wants the new yeast to grow some oxygen must remain in solution. Alternatively one can pitch a very concentrated yeast starter that already has sufficient yeast to do the fermenting without the need to grow/multiply.

Of course the original wort may have had a higher percentage of unfermentable poly-saccharides (eg starch and malto-dextrins) and that is the reason the fermentation has stopped - it has run out of fermentable sugars. One way to improve this situation might be to add some pilsner enzyme to break down the poly saccharides to simpler sugars which can be fermented. That would probably require some lagering for it all to take effect and proceed to completion.

Good luck!

It looks like you aren't the only one having this problem, however it may just be that it's finished:

http://www.homebrewtalk.com/showthread.php?t=161961

http://www.homebrewtalk.com/showthread.php?t=376552

If you wanted to be sure, you can just pitch the yeast in directly... from what I have read, starters aren't needed for pitching dried packet yeast.