Hi fiona
I'm really sorry to hear about what has happened.
At the risk of stating the obvious, the first thing I'd do is contact Dogs Lost UK. Put the following link in and go from there.
http://www.doglost.co.uk/default.asp
Did you lose them in the area you live? If so, do some posters with their photos on. Are the dogs insured? If so, some insurance companies will fund a reward on the safe return. If they're not insured, you may want to consider offering a financial reward.
Drive round to your local pet shops and vets and put posters up in there (with photos of the dogs on). Contact your local RSPCA, dog warden and police. At the risk of sounding grim, also contact your local council as if god forbid, the dogs have been run over, the council will pick them up if they have been left by the roadside.
If it was me, I'd be straight onto my local paper and ask them to do a piece about it. I'd also contact the local radio station too.
Are they micro chipped or tattooed?
Finally, I am a member of several canine forums, if you can give me more information, I will put a notice on there for you. It would be helpful to have photos too.
I know someone who breeds lakelands and is into rescue, so when you give me more information, I'll contact her as well to see if she can offer any advice.
Can you tell me what you have done in the meantime to try and find them?
Lisa