Depending on where seller is shipping from, your item could very well in transit. Dont panic. If from Canada, it may very well arrive in the next day or two. Not all sellers mark the item as having been shipped.
If from outside Canada, another country's postal service handles things until it gets to our border. Then it can get stuck at customs. If it has only been a week, things are fine. Messaging the seller is fine, if you are just inquiring about whether the item has been shipped. If you paid with Paypal, you still have a long time left to open a dispute . Give it a bit more time.
If you still havent received it in a week or so, post another message on here. To make things easier, post the item number as well. This allows anyone reading the post to search that item, bring up the listing, see where it is coming from and shipping method, including handling time.
Rick
"Egotism is the anesthetic that dulls the pain of stupidity" - Frank Leahy