Can I swap down to a different number of teeth on a chainring I currently have a single speed front chainring setup with 52 teeth. I can't find a suitable replacement for my chainring so I am wondering if it is possible to get a chainring with a different  number of teeth, e.g. 48 teeth.
Yes, this should be possible. Though there are several things you need to check to ensure it is compatible:


Number of bolts, and bolt circle diameter (BCD). Count the number of bolts, and measure the distance between the centre of two bolts. Then check Sheldon Brown's Bolt Circle Diameter Crib Sheet to see what the BCD is. Common sizes are 110 (mountain bike), 130 (road), 135 (Campagnolo) or 144 (track).
Chain width. Most bicycle chains are 3/32" wide, though some singlespeeds use wider 1/8" chains. You want the chain, chainring and sprocket to be the same width. Wider chains and chainrings may last longer, though are a bit heavier.
Chainring ramps. Most chainrings are designed for geared bikes, so have 'ramps' to allow the chain to derail and change from one ring to the other. If the bike is singlespeed, you don't want this, so look for an unramped or singlespeed specific chainring.
Chain length. If changing to a smaller chainring, your chain will have to be a bit shorter. So you will have to remove a couple of links from the chain, or adjust your chain tensioner if you are using one. Note if your chainring is worn out, then your chain is probably also worn. So it would be worth replacing the chain with a new one.
Gear ratio. For a singlespeed, changing to a smaller chainring will give you a lower gear ratio. So you will have to pedal faster to go at the same speed. This may be preferred, depending on what sort of terrain you ride on, and how fast a cadence you like. If you want to keep a similar gear, you can change the rear sprocket to a larger size.