'Lost Sheep' in the Bible

I have gone astray like a lost sheep: seek thy servant; for I have not forgotten thy commandments.

My people are lost sheep; their shepherds have caused them to go astray, they turned them away on the mountains: they went from mountain to hill, they forgot their resting-place.

but go rather to the lost sheep of the house of Israel.

But he answering said, I have not been sent save to the lost sheep of Israel's house.

and being come to the house, calls together the friends and the neighbours, saying to them, Rejoice with me, for I have found my lost sheep.