We had two kinds of stickers in this yard when we moved in. One was a garden escapee that was easy to identify and pull. Within one growing season it was eradicated. The other was the common sand burr, which we will always have to watch for as it is carried from neighboring yards, but is contained
enough for us to send barefoot children to play in our own yard.
If you can post a picture of the sticker it may help identify it. Without an identification, you might be able to make some temporary headway using the one we employed with the sand burrs. When you step upon one of the stickers, take an old terry cloth that is destined for rags and drag it vigorously across the lawn in that area. It
should look like you're seriously scrubbing the dirt clean. This should capture the remaining stickers in the area so that you can dispose of them. Consider the terry cloth a sacrifice to the gods in lieu of blood shed.
Mark that area of the lawn and keep a close eye on all developing plants to see if you can identify any new stickers forming. If it is an annual, you may be lucky enough to end the cycle there. It a
perennial, then you can locate your target and do some dedicated weeding. You really can weed stickers out a lawn, once you identify the plants.