Regex match for beginning of multiple words in string

In Javascript i want to be able to match strings that begin with a certain phrase. However, I want it to be able to match the start of any word in the phrase, not just the beginning of the phrase.

For example:

Phrase: "This is the best"

Need to Match: "th"

Result: Matches Th and th

EDIT: \b works great however it proposes another issue:

It will also match characters after foreign ones. For example if my string is "Männ", and i search for "n", it will match the n after Mä...Any ideas?