Couple of notes, please don't reply to threads just to bump them to top of list especially if the last reply is only a few days old. Of course if you have something to add in your reply that's fine.
For your own topics you have started If you want to bump a it to the top of the forum to get some attention on something that was overlooked after 24 hours with no replies a link will appear "Bump topic" down the bottom left near the "subscribe topic" link. This has same effect as replying to topic and will send it to the top of the list. The link will not appear again until the 24 hour time limit is up.