This is called a recruiter. I've used them in the UK and they were great. Didn't mess with my CV as far as I know and they were very helpful in suggesting suitable companies, skipping the HR filter, and telling me what to expect in the interviews.
However I work in a pretty niche industry (silicon verification) and I didn't seek them out - I get a few emails a month on LinkedIn from various recruiters and hiring people and I just responded to some.
So it probably depends on what experience you have and what industry you're in. I would definitely recommend keeping your LinkedIn up-to-date though.