Sorry, it's the opposite, haha. A torrent file is basically a node. When you put it in your client, it does two things: leech and seed. Leeching means it's downloading bits from other people, seeding means that other people are downloading bits from you. The torrent file essentially directs your client to other people's files, then flags the files you've downloaded for others to take. If there are a lot of seeders, you get to download pieces from each of them at once, which makes the process go faster, since the load is divided among many different people. When more people are leeching, that effect is reduced. If you leave a torrent file when you're done downloading in whatever client you're using, it will start seeding to other people. Some private torrent sites require you to keep up a ratio from seeding/leeching to make sure users are giving back to the community.
Basically, something will download faster when there's a lot of seeders and few leechers.
That is a good simplistic view, but it doesn't actually quite work that way. For one, when you're leeching a file, your torrent client is actually already seeding your completed pieces (each torrent gets chopped into pieces and the tracker keeps track of which ones you have and which ones you need). So really, adding peers to a torrent shouldn't theoretically slow it down, because even if those peers are "stealing" bandwidth from the seeder(s), they should pass on anything they already obtained to you. Trackers are actually pretty sophisticated and will try to distribute pieces that have the least available copies so that new content gets pushed to peers and the peers can share with each other, even if none of them have the full file.
But actually, It could really help to have more peers on a torrent. First of all, if the peers are not maxing out the seeders' upload bandwidth, then more peers means even more unique pieces to share and more copies of each piece will be available. This is important because of many factors, but a good example is that torrent clients use metrics to determine how good your connection is to other peers (ping, connectivity in general, data loss, transfer speed, etc). If you have a crappy connection to someone, or if they have no data you are interested in (meaning they have no pieces of the torrent you still need), their rating will go down and you may not get connected to them, thus hampering both your download and the overall seeding of the torrent. Add to that the fact that many torrent clients are configured to have download and upload slot limits, and you can imagine how fewer peers can cause bottlenecks and non-ideal conditions. The more there are, the more chances there are to find good matches and spread the data across many computers.
The short answer is that yes, if you got a bunch of friends to jump on a poorly seeded torrent, you will probably see some kind of performance increase. At worst it would be the same (like if, say, there is only 1 seed and he has terrible upload capabilities).