Femke is a Frisian and Dutch name — the diminutive of Femme, from Old Frisian fem (maiden) or frem (peace, stranger).
Femke is widely used in the Netherlands and northern Germany. Femke Halsema (born 1966), the mayor of Amsterdam from 2018, is a contemporary bearer.
Femke does not currently appear in the US Social Security Administration's top 1,000 girls' names, so we don't publish a US rank or birth count for it. That says nothing about the name's standing elsewhere in the world — only that it sits outside the ranked US data we rely on.
In Pythagorean numerology the letters of Femke reduce to 4, The Builder. This is a traditional interpretive system, not a factual claim about the name.