Sprinkling some new yeast into a stuck fermentation is rarely going to save the beer. The yeast that you started with have already taken up all the nutrients and had time to acclimate to the new low-nutrient, low-oxygen, alcoholic environment. Generally, your best bet is to get the yeast you pitched initially back on the job by warming the beer and rousing the yeast gently. If you MUST repitch, pitching yeast from a small starter that is at peak activity would give you the best shot at giving it a chance to make a difference - at that point, it's active and much more ready for the environment you are about to toss it into.
We need the deets, mon ami!
What was your recipe? That can help determine if perhaps you had a bad OG reading - it's not uncommon to have a false reading due to doing a partial boil and getting either a very watery or very syrupy sample.
Extract or all-grain? Again, sometimes extract doesn't get evenly distributed - generally this is a factor if you do a late addition as opposed to boiling all of the extract from the very beginning and it can throw off your OG reading.
If it was all-grain, what was your mash temp? High temps can result in fewer fermentable sugars in your wort, thus a higher FG.
Finally, as McKnuckle asked in the post above mine, what are you using to measure gravity? Refractometers need a correction to the reading once alcohol is present, and they can be a common culprit for strange FG readings when the correction isn't taken into consideration.
